diff --git a/Common/Orders/BloombergFixOrderProperties.cs b/Common/Orders/BloombergFixOrderProperties.cs
index 7a77f2d7423c..6565bf2259dd 100644
--- a/Common/Orders/BloombergFixOrderProperties.cs
+++ b/Common/Orders/BloombergFixOrderProperties.cs
@@ -13,8 +13,6 @@
  * limitations under the License.
 */
 
-using System.Collections.Generic;
-
 namespace QuantConnect.Orders
 {
     /// <summary>
@@ -28,7 +26,7 @@ public class BloombergFixOrderProperties : FixOrderProperties
         /// </summary>
         public string LocateBroker
         {
-            get { return AdditionalProperties?.GetValueOrDefault("5700"); }
+            get { return GetTag("5700"); }
             set { SetTag("5700", value); }
         }
 
@@ -38,10 +36,15 @@ public string LocateBroker
         /// </summary>
         public string LocateReqd
         {
-            get { return AdditionalProperties?.GetValueOrDefault("114"); }
+            get { return GetTag("114"); }
             set { SetTag("114", value); }
         }
 
+        private string GetTag(string tag)
+        {
+            return AdditionalProperties != null && AdditionalProperties.TryGetValue(tag, out var value) ? value : null;
+        }
+
         private void SetTag(string tag, string value)
         {
             if (value == null)
diff --git a/Common/Orders/FixOrderProperties.cs b/Common/Orders/FixOrderProperties.cs
index 077ca5a75c20..1e9cd4770d00 100644
--- a/Common/Orders/FixOrderProperties.cs
+++ b/Common/Orders/FixOrderProperties.cs
@@ -13,7 +13,7 @@
  * limitations under the License.
 */
 
-using System.Collections.Generic;
+using Common.Util;
 using QuantConnect.Interfaces;
 
 namespace QuantConnect.Orders
@@ -27,7 +27,10 @@ public class FixOrderProperties : OrderProperties
         /// Custom FIX tags to send with the order. The key is the FIX tag number
         /// and the value is the tag value, e.g. AdditionalProperties["9301"] = "1"
         /// </summary>
-        public Dictionary<string, string> AdditionalProperties { get; set; } = [];
+        /// <remarks>Starts empty. Python cannot assign a plain dict to it, since pythonnet has no
+        /// conversion for it; add the entries one by one, bulk load them from a dict with update(),
+        /// and reset with clear()</remarks>
+        public BaseExtendedDictionary<string, string> AdditionalProperties { get; set; } = [];
 
         /// <summary>
         /// Instruction for order handling on Broker floor
@@ -60,7 +63,7 @@ public class FixOrderProperties : OrderProperties
         public override IOrderProperties Clone()
         {
             var clone = (FixOrderProperties)MemberwiseClone();
-            clone.AdditionalProperties = new Dictionary<string, string>(AdditionalProperties);
+            clone.AdditionalProperties = new BaseExtendedDictionary<string, string>(AdditionalProperties);
             return clone;
         }
     }
diff --git a/Common/Orders/TerminalLinkOrderProperties.cs b/Common/Orders/TerminalLinkOrderProperties.cs
index 333133dc0fa0..db0a52dffb1b 100644
--- a/Common/Orders/TerminalLinkOrderProperties.cs
+++ b/Common/Orders/TerminalLinkOrderProperties.cs
@@ -15,6 +15,8 @@
 */
 
 using System.Collections.Generic;
+using Common.Util;
+using QuantConnect.Interfaces;
 
 namespace QuantConnect.Orders
 {
@@ -23,6 +25,15 @@ namespace QuantConnect.Orders
     /// </summary>
     public class TerminalLinkOrderProperties : OrderProperties
     {
+        /// <summary>
+        /// Custom EMSX fields to send with the order. The key is the EMSX element name
+        /// and the value is the element value, e.g. AdditionalProperties["EMSX_CFD_FLAG"] = "1"
+        /// </summary>
+        /// <remarks>Starts empty. Python cannot assign a plain dict to it, since pythonnet has no
+        /// conversion for it; add the entries one by one, bulk load them from a dict with update(),
+        /// and reset with clear()</remarks>
+        public BaseExtendedDictionary<string, string> AdditionalProperties { get; set; } = [];
+
         /// <summary>
         /// The EMSX Instructions is the free form instructions that may be sent to the broker
         /// </summary>
@@ -88,6 +99,17 @@ public class TerminalLinkOrderProperties : OrderProperties
         /// </summary>
         public string LocateId { get; set; }
 
+        /// <summary>
+        /// Indicates if the order is a contract for differences (CFD) trade (EMSX_CFD_FLAG).
+        /// This field is applicable to trades on an order level, and does not populate on a per
+        /// security basis.
+        /// </summary>
+        public bool IsCfdTrade
+        {
+            get { return AdditionalProperties != null && AdditionalProperties.TryGetValue("EMSX_CFD_FLAG", out var flag) && flag == "1"; }
+            set { SetTag("EMSX_CFD_FLAG", value ? "1" : null); }
+        }
+
         /// <summary>
         /// The EMSX order strategy details.
         /// Strategy parameters must be appended in the correct order as expected by EMSX.
@@ -105,6 +127,31 @@ public class TerminalLinkOrderProperties : OrderProperties
         /// <remarks>Has precedence over <see cref="AutomaticPositionSides"/></remarks>
         public OrderPosition? PositionSide { get; set; }
 
+        /// <summary>
+        /// Returns a new instance clone of this object
+        /// </summary>
+        /// <remarks>Deep copies <see cref="AdditionalProperties"/> so edits on the clone, e.g. the
+        /// locate cleanup in BrokerageExtensions.RemoveLocateFromNonShortOrder, never reach the
+        /// instance the algorithm holds on to</remarks>
+        public override IOrderProperties Clone()
+        {
+            var clone = (TerminalLinkOrderProperties)MemberwiseClone();
+            clone.AdditionalProperties = new BaseExtendedDictionary<string, string>(AdditionalProperties);
+            return clone;
+        }
+
+        private void SetTag(string tag, string value)
+        {
+            if (value == null)
+            {
+                AdditionalProperties?.Remove(tag);
+            }
+            else
+            {
+                AdditionalProperties[tag] = value;
+            }
+        }
+
         /// <summary>
         /// Models an EMSX order strategy parameter
         /// </summary>
diff --git a/Tests/Common/Orders/FixOrderPropertiesTests.cs b/Tests/Common/Orders/FixOrderPropertiesTests.cs
index 9105fe89db3d..6991a5844c40 100644
--- a/Tests/Common/Orders/FixOrderPropertiesTests.cs
+++ b/Tests/Common/Orders/FixOrderPropertiesTests.cs
@@ -14,6 +14,7 @@
 */
 
 using NUnit.Framework;
+using Python.Runtime;
 using QuantConnect.Interfaces;
 using QuantConnect.Orders;
 
@@ -37,5 +38,48 @@ public void BloombergFixOrderPropertiesSupportsAdditionalPropertiesAndClone()
             properties.AdditionalProperties["9301"] = "2";
             Assert.AreEqual("1", clone.AdditionalProperties["9301"]);
         }
+
+        [Test]
+        public void LocateTagPassthroughsSurviveTheDictionarySwap()
+        {
+            // The tags are the store behind the properties, so writing either way must be visible
+            // from the other.
+            var properties = new BloombergFixOrderProperties { LocateBroker = "MLCO" };
+            Assert.AreEqual("MLCO", properties.AdditionalProperties["5700"]);
+
+            properties.AdditionalProperties["114"] = "Y";
+            Assert.AreEqual("Y", properties.LocateReqd);
+
+            properties.LocateBroker = null;
+            Assert.IsFalse(properties.AdditionalProperties.ContainsKey("5700"));
+            Assert.IsNull(properties.LocateBroker);
+        }
+
+        [Test]
+        public void UpdatesAdditionalPropertiesFromPlainPythonDictionary()
+        {
+            using (Py.GIL())
+            {
+                // pythonnet cannot convert a plain dict for assignment, so update() is what lets a
+                // Python algorithm bulk load its custom tags.
+                var module = PyModule.FromString("fixAdditionalPropertiesModule",
+                    @"
+from AlgorithmImports import *
+
+def getOrderProperties() -> BloombergFixOrderProperties:
+    properties = BloombergFixOrderProperties()
+    properties.additional_properties.update({ ""5700"": ""MLCO"", ""9301"": ""1"" })
+    return properties
+");
+
+                dynamic getOrderProperties = module.GetAttr("getOrderProperties");
+                var properties = (BloombergFixOrderProperties)getOrderProperties();
+
+                Assert.IsNotNull(properties);
+                Assert.AreEqual(2, properties.AdditionalProperties.Count);
+                Assert.AreEqual("1", properties.AdditionalProperties["9301"]);
+                Assert.AreEqual("MLCO", properties.LocateBroker);
+            }
+        }
     }
 }
diff --git a/Tests/Common/Orders/TerminalLinkOrderPropertiesTests.cs b/Tests/Common/Orders/TerminalLinkOrderPropertiesTests.cs
index df86a02882d1..e3ea4e325d50 100644
--- a/Tests/Common/Orders/TerminalLinkOrderPropertiesTests.cs
+++ b/Tests/Common/Orders/TerminalLinkOrderPropertiesTests.cs
@@ -13,6 +13,7 @@
  * limitations under the License.
 */
 
+using System;
 using NUnit.Framework;
 using Python.Runtime;
 using QuantConnect.Orders;
@@ -100,5 +101,181 @@ def getOrderProperties() -> TerminalLinkOrderProperties:
                 Assert.AreEqual("LOC-123", properties.LocateId);
             }
         }
+
+        [Test]
+        public void IsCfdTradeDefaultsToFalse()
+        {
+            // A regular trade is the EMSX default, and the value for which the brokerage sends no
+            // EMSX_CFD_FLAG at all, so it must be what an untouched instance reports.
+            var properties = new TerminalLinkOrderProperties();
+            Assert.IsFalse(properties.IsCfdTrade);
+        }
+
+        [Test]
+        public void CloneDoesNotShareAdditionalProperties()
+        {
+            // Order properties are reused across orders and cloned before being edited, e.g. by
+            // BrokerageExtensions.RemoveLocateFromNonShortOrder; a shared dictionary would let an
+            // edit on the copy leak back into the caller's instance.
+            var properties = new TerminalLinkOrderProperties { IsCfdTrade = true };
+
+            var clone = (TerminalLinkOrderProperties)properties.Clone();
+            clone.IsCfdTrade = false;
+
+            Assert.IsTrue(properties.IsCfdTrade);
+        }
+
+        [Test]
+        public void SetsIsCfdTradeFromPython()
+        {
+            using (Py.GIL())
+            {
+                var module = PyModule.FromString("cfdTradeModule",
+                    @"
+from AlgorithmImports import *
+
+def getOrderProperties() -> TerminalLinkOrderProperties:
+    properties = TerminalLinkOrderProperties()
+    properties.is_cfd_trade = True
+    return properties
+");
+
+                dynamic getOrderProperties = module.GetAttr("getOrderProperties");
+                var properties = (TerminalLinkOrderProperties)getOrderProperties();
+
+                Assert.IsNotNull(properties);
+                Assert.IsTrue(properties.IsCfdTrade);
+            }
+        }
+
+        [Test]
+        public void SetsAdditionalPropertiesEntryFromPython()
+        {
+            using (Py.GIL())
+            {
+                var module = PyModule.FromString("additionalPropertiesEntryModule",
+                    @"
+from AlgorithmImports import *
+
+def getOrderProperties() -> TerminalLinkOrderProperties:
+    properties = TerminalLinkOrderProperties()
+    properties.additional_properties[""EMSX_CFD_FLAG""] = ""1""
+    properties.additional_properties[""EMSX_ODD_LOT""] = ""0""
+    return properties
+");
+
+                dynamic getOrderProperties = module.GetAttr("getOrderProperties");
+                var properties = (TerminalLinkOrderProperties)getOrderProperties();
+
+                Assert.IsNotNull(properties);
+                Assert.AreEqual(2, properties.AdditionalProperties.Count);
+                Assert.AreEqual("0", properties.AdditionalProperties["EMSX_ODD_LOT"]);
+                // an entry written through the dictionary is visible on the typed property
+                Assert.IsTrue(properties.IsCfdTrade);
+            }
+        }
+
+        [Test]
+        public void ClearsAdditionalPropertiesFromPython()
+        {
+            using (Py.GIL())
+            {
+                // clear() resets the dictionary, taking the typed properties reading from it back to
+                // their defaults.
+                var module = PyModule.FromString("additionalPropertiesClearModule",
+                    @"
+from AlgorithmImports import *
+
+def getOrderProperties() -> TerminalLinkOrderProperties:
+    properties = TerminalLinkOrderProperties()
+    properties.is_cfd_trade = True
+    properties.additional_properties[""EMSX_ODD_LOT""] = ""0""
+    properties.additional_properties.clear()
+    return properties
+");
+
+                dynamic getOrderProperties = module.GetAttr("getOrderProperties");
+                var properties = (TerminalLinkOrderProperties)getOrderProperties();
+
+                Assert.IsNotNull(properties);
+                Assert.IsEmpty(properties.AdditionalProperties);
+                Assert.IsFalse(properties.IsCfdTrade);
+            }
+        }
+
+        [Test]
+        public void UpdatesAdditionalPropertiesFromPlainPythonDictionary()
+        {
+            using (Py.GIL())
+            {
+                // update() is the way to bulk load from a plain Python dict; it takes a PyObject, so
+                // it sidesteps the conversion that plain assignment cannot do.
+                var module = PyModule.FromString("additionalPropertiesUpdateModule",
+                    @"
+from AlgorithmImports import *
+
+def getOrderProperties() -> TerminalLinkOrderProperties:
+    properties = TerminalLinkOrderProperties()
+    properties.additional_properties.update({ ""EMSX_CFD_FLAG"": ""1"", ""EMSX_ODD_LOT"": ""0"" })
+    return properties
+");
+
+                dynamic getOrderProperties = module.GetAttr("getOrderProperties");
+                var properties = (TerminalLinkOrderProperties)getOrderProperties();
+
+                Assert.IsNotNull(properties);
+                Assert.AreEqual(2, properties.AdditionalProperties.Count);
+                Assert.AreEqual("0", properties.AdditionalProperties["EMSX_ODD_LOT"]);
+                Assert.IsTrue(properties.IsCfdTrade);
+            }
+        }
+
+        [Test]
+        public void AssigningPlainPythonDictionaryToAdditionalPropertiesThrows()
+        {
+            using (Py.GIL())
+            {
+                // pythonnet has no conversion from a Python dict to Dictionary<string, string>, so
+                // the natural looking assignment fails at runtime; the entries have to be added to
+                // the dictionary the properties already own.
+                var module = PyModule.FromString("additionalPropertiesReplacementModule",
+                    @"
+from AlgorithmImports import *
+
+def getOrderProperties() -> TerminalLinkOrderProperties:
+    properties = TerminalLinkOrderProperties()
+    properties.additional_properties = { ""EMSX_CFD_FLAG"": ""1"" }
+    return properties
+");
+
+                dynamic getOrderProperties = module.GetAttr("getOrderProperties");
+
+                var exception = Assert.Throws<PythonException>(() => getOrderProperties());
+                Assert.IsTrue(exception.Message.Contains("cannot be converted", StringComparison.InvariantCulture),
+                    $"Expected a conversion failure, got: {exception.Message}");
+            }
+        }
+
+        [Test]
+        public void ReadsAdditionalPropertiesEntryWrittenByTypedPropertyFromPython()
+        {
+            using (Py.GIL())
+            {
+                var module = PyModule.FromString("additionalPropertiesReadModule",
+                    @"
+from AlgorithmImports import *
+
+def getCfdFlag() -> str:
+    properties = TerminalLinkOrderProperties()
+    properties.is_cfd_trade = True
+    return properties.additional_properties[""EMSX_CFD_FLAG""]
+");
+
+                dynamic getCfdFlag = module.GetAttr("getCfdFlag");
+                var flag = (string)getCfdFlag();
+
+                Assert.AreEqual("1", flag);
+            }
+        }
     }
 }
diff --git a/Tests/Engine/BrokerageTransactionHandlerTests/BrokerageTransactionHandlerTests.cs b/Tests/Engine/BrokerageTransactionHandlerTests/BrokerageTransactionHandlerTests.cs
index 35cf8275e617..a7c22d903ec1 100644
--- a/Tests/Engine/BrokerageTransactionHandlerTests/BrokerageTransactionHandlerTests.cs
+++ b/Tests/Engine/BrokerageTransactionHandlerTests/BrokerageTransactionHandlerTests.cs
@@ -396,11 +396,17 @@ private static (string LocateBroker, string LocateId, string LocateBrokerTag, st
             {
                 TerminalLinkOrderProperties terminalLink => (terminalLink.LocateBroker, terminalLink.LocateId, null, null),
                 WolverineOrderProperties wolverine => (wolverine.LocateBroker, null, null, null),
-                FixOrderProperties fix => (null, null, fix.AdditionalProperties.GetValueOrDefault("5700"), fix.AdditionalProperties.GetValueOrDefault("114")),
+                FixOrderProperties fix => (null, null, GetTag(fix, "5700"), GetTag(fix, "114")),
                 _ => default
             };
         }
 
+        private static string GetTag(FixOrderProperties properties, string tag)
+        {
+            properties.AdditionalProperties.TryGetValue(tag, out var value);
+            return value;
+        }
+
         private static BloombergFixOrderProperties CreateLocateBrokerTagProperties()
         {
             // the property is a passthrough of the 5700 tag in AdditionalProperties