diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/InstanceCommands.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/InstanceCommands.cs
index 9e13c71f..e7fcb0e9 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/InstanceCommands.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Messages/Management/InstanceCommands.cs
@@ -12,8 +12,17 @@ public record MgmtDeleteInstanceCommand(int InstanceId);
 /// <see cref="SetConnectionBindingsCommand"/>. This is a named record (not a
 /// <c>ValueTuple</c>) so it serializes with stable, named JSON properties and can
 /// evolve additively per REQ-COM-5a.
+/// <para>
+/// <c>DataSourceReferenceOverride</c> is an optional per-instance override of
+/// the OPC UA node id (or other protocol address) for the bound attribute.
+/// When non-null it replaces the template's <c>DataSourceReference</c> at
+/// flattening time; when null the template default is used.
+/// </para>
 /// </summary>
-public record ConnectionBinding(string AttributeName, int DataConnectionId);
+public record ConnectionBinding(
+    string AttributeName,
+    int DataConnectionId,
+    string? DataSourceReferenceOverride = null);
 
 public record SetConnectionBindingsCommand(int InstanceId, IReadOnlyList<ConnectionBinding> Bindings);
 public record SetInstanceOverridesCommand(int InstanceId, IReadOnlyDictionary<string, string?> Overrides);
diff --git a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Services/InstanceService.cs b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Services/InstanceService.cs
index 0dd483a5..1c69a847 100644
--- a/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Services/InstanceService.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.TemplateEngine/Services/InstanceService.cs
@@ -330,20 +330,22 @@ public class InstanceService
 
         var results = new List<InstanceConnectionBinding>();
 
-        foreach (var (attrName, connId) in bindings)
+        foreach (var b in bindings)
         {
-            if (existingMap.TryGetValue(attrName, out var existing))
+            if (existingMap.TryGetValue(b.AttributeName, out var existing))
             {
-                existing.DataConnectionId = connId;
+                existing.DataConnectionId = b.DataConnectionId;
+                existing.DataSourceReferenceOverride = b.DataSourceReferenceOverride;
                 await _repository.UpdateInstanceConnectionBindingAsync(existing, cancellationToken);
                 results.Add(existing);
             }
             else
             {
-                var binding = new InstanceConnectionBinding(attrName)
+                var binding = new InstanceConnectionBinding(b.AttributeName)
                 {
                     InstanceId = instanceId,
-                    DataConnectionId = connId
+                    DataConnectionId = b.DataConnectionId,
+                    DataSourceReferenceOverride = b.DataSourceReferenceOverride
                 };
                 await _repository.AddInstanceConnectionBindingAsync(binding, cancellationToken);
                 results.Add(binding);
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Messages/ConnectionBindingSerializationTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Messages/ConnectionBindingSerializationTests.cs
index 9a7e504c..856aaf5a 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Messages/ConnectionBindingSerializationTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Messages/ConnectionBindingSerializationTests.cs
@@ -51,4 +51,32 @@ public class ConnectionBindingSerializationTests
         // ConnectionBinding is a record: each element compares by value.
         Assert.Equal(original.Bindings, deserialized.Bindings);
     }
+
+    [Fact]
+    public void Roundtrip_preserves_override_when_set()
+    {
+        var original = new ConnectionBinding("Speed", 7, "ns=2;s=Pump1.Speed");
+
+        var json = JsonSerializer.Serialize(original);
+        var roundtripped = JsonSerializer.Deserialize<ConnectionBinding>(json);
+
+        Assert.NotNull(roundtripped);
+        Assert.Equal(original, roundtripped);
+        Assert.Equal("ns=2;s=Pump1.Speed", roundtripped!.DataSourceReferenceOverride);
+    }
+
+    [Fact]
+    public void Roundtrip_defaults_override_to_null_when_absent()
+    {
+        // Older site builds will not emit the new field — deserialization
+        // must produce a null override and equal an explicit-null instance.
+        const string legacyJson = """{"AttributeName":"Speed","DataConnectionId":7}""";
+
+        var deserialized = JsonSerializer.Deserialize<ConnectionBinding>(legacyJson);
+
+        Assert.NotNull(deserialized);
+        Assert.Equal("Speed", deserialized!.AttributeName);
+        Assert.Equal(7, deserialized.DataConnectionId);
+        Assert.Null(deserialized.DataSourceReferenceOverride);
+    }
 }