diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs
index bda644cd..eda6f98f 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs
@@ -77,15 +77,19 @@ public sealed class Phase7Applier
             plan.AddedEquipmentTags.Count +
             plan.AddedEquipmentVirtualTags.Count;
 
-        // Any add/remove of Equipment, ScriptedAlarm, Equipment tag, or Equipment VirtualTag topology
-        // requires a real address-space rebuild. Driver-instance changes don't touch the address-space
-        // topology directly — they go through DriverHostActor's spawn-plan in Runtime.
-        // TODO(equipment-virtualtags): when MaterialiseEquipmentVirtualTags drives per-delta sink work, revisit whether ChangedEquipmentVirtualTags should also force needsRebuild.
+        // Any add / remove / in-place CHANGE of Equipment, ScriptedAlarm, Equipment tag, or Equipment
+        // VirtualTag topology requires a real address-space rebuild — the materialise passes re-derive
+        // every node from the composition, so a changed-only deploy (e.g. a renamed equipment, a
+        // re-severitied alarm, a flipped tag dataType/Writable, or an edited VirtualTag expression) must
+        // still rebuild or the running server keeps the stale node.
+        // ChangedDrivers is deliberately EXCLUDED: a driver-instance config change doesn't touch the
+        // address-space topology — it routes through DriverHostActor's spawn-plan in Runtime, which
+        // re-spawns the affected driver actor without re-materialising any nodes.
         var needsRebuild =
-            plan.AddedEquipment.Count > 0 || plan.RemovedEquipment.Count > 0 ||
-            plan.AddedAlarms.Count > 0 || plan.RemovedAlarms.Count > 0 ||
-            plan.AddedEquipmentTags.Count > 0 || plan.RemovedEquipmentTags.Count > 0 ||
-            plan.AddedEquipmentVirtualTags.Count > 0 || plan.RemovedEquipmentVirtualTags.Count > 0;
+            plan.AddedEquipment.Count > 0 || plan.RemovedEquipment.Count > 0 || plan.ChangedEquipment.Count > 0 ||
+            plan.AddedAlarms.Count > 0 || plan.RemovedAlarms.Count > 0 || plan.ChangedAlarms.Count > 0 ||
+            plan.AddedEquipmentTags.Count > 0 || plan.RemovedEquipmentTags.Count > 0 || plan.ChangedEquipmentTags.Count > 0 ||
+            plan.AddedEquipmentVirtualTags.Count > 0 || plan.RemovedEquipmentVirtualTags.Count > 0 || plan.ChangedEquipmentVirtualTags.Count > 0;
 
         if (needsRebuild)
         {
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
index b30c6403..c794bfce 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
@@ -498,6 +498,153 @@ public sealed class Phase7ApplierTests
         sink.RebuildCalls.ShouldBe(1);
     }
 
+    /// <summary>H1a — a deploy that ONLY changes an existing equipment tag (e.g. flips its dataType or
+    /// Writable bit) must rebuild the address space. The planner diffs the tag into
+    /// <c>ChangedEquipmentTags</c> with no Added/Removed of anything else; the applier must still drive
+    /// exactly one rebuild so the running server drops the stale node and re-materialises it.</summary>
+    [Fact]
+    public void Changed_equipment_tags_only_trigger_rebuild()
+    {
+        var sink = new RecordingSink();
+        var applier = new Phase7Applier(sink, NullLogger<Phase7Applier>.Instance);
+
+        var previous = CompositionWithTags(
+            new EquipmentTagPlan("tag-1", "eq-1", "drv", FolderPath: "", Name: "Speed", DataType: "Float", FullName: "40001", Writable: false, Alarm: null));
+        // Same tag id, but DataType + Writable flipped — the planner classifies this as a change.
+        var next = CompositionWithTags(
+            new EquipmentTagPlan("tag-1", "eq-1", "drv", FolderPath: "", Name: "Speed", DataType: "Int32", FullName: "40001", Writable: true, Alarm: null));
+
+        var plan = Phase7Planner.Compute(previous, next);
+
+        // Guard the arrange: ONLY ChangedEquipmentTags is populated.
+        plan.ChangedEquipmentTags.Count.ShouldBe(1);
+        plan.AddedEquipmentTags.ShouldBeEmpty();
+        plan.RemovedEquipmentTags.ShouldBeEmpty();
+        plan.AddedEquipment.ShouldBeEmpty();
+        plan.RemovedEquipment.ShouldBeEmpty();
+
+        var outcome = applier.Apply(plan);
+
+        outcome.RebuildCalled.ShouldBeTrue();
+        outcome.ChangedNodes.ShouldBe(1);
+        sink.RebuildCalls.ShouldBe(1);
+    }
+
+    /// <summary>H1a — a deploy that ONLY edits an existing VirtualTag's expression must rebuild the
+    /// address space. The planner diffs it into <c>ChangedEquipmentVirtualTags</c> alone; the applier
+    /// must drive exactly one rebuild.</summary>
+    [Fact]
+    public void Changed_equipment_virtual_tags_only_trigger_rebuild()
+    {
+        var sink = new RecordingSink();
+        var applier = new Phase7Applier(sink, NullLogger<Phase7Applier>.Instance);
+
+        var previous = CompositionWithVirtualTags(
+            new EquipmentVirtualTagPlan("vt-1", "eq-1", FolderPath: "", Name: "Efficiency", DataType: "Float64",
+                Expression: "ctx.GetTag(\"a\") * 60", DependencyRefs: new[] { "a" }));
+        // Same VirtualTag id, edited expression — the planner classifies this as a change.
+        var next = CompositionWithVirtualTags(
+            new EquipmentVirtualTagPlan("vt-1", "eq-1", FolderPath: "", Name: "Efficiency", DataType: "Float64",
+                Expression: "ctx.GetTag(\"a\") * 120", DependencyRefs: new[] { "a" }));
+
+        var plan = Phase7Planner.Compute(previous, next);
+
+        // Guard the arrange: ONLY ChangedEquipmentVirtualTags is populated.
+        plan.ChangedEquipmentVirtualTags.Count.ShouldBe(1);
+        plan.AddedEquipmentVirtualTags.ShouldBeEmpty();
+        plan.RemovedEquipmentVirtualTags.ShouldBeEmpty();
+
+        var outcome = applier.Apply(plan);
+
+        outcome.RebuildCalled.ShouldBeTrue();
+        outcome.ChangedNodes.ShouldBe(1);
+        sink.RebuildCalls.ShouldBe(1);
+    }
+
+    /// <summary>H1a — a deploy that ONLY edits an existing scripted alarm (here its message template)
+    /// must rebuild the address space. The planner diffs the thin <c>ScriptedAlarmPlan</c> projection
+    /// into <c>ChangedAlarms</c> alone; the applier must drive exactly one rebuild so the condition node
+    /// reflects the edit.</summary>
+    [Fact]
+    public void Changed_alarms_only_trigger_rebuild()
+    {
+        var sink = new RecordingSink();
+        var applier = new Phase7Applier(sink, NullLogger<Phase7Applier>.Instance);
+
+        var previous = CompositionWithAlarms(new ScriptedAlarmPlan("alm-1", "eq-1", "scr-1", "Temp high"));
+        // Same alarm id, edited message template — the planner classifies this as a change.
+        var next = CompositionWithAlarms(new ScriptedAlarmPlan("alm-1", "eq-1", "scr-1", "Temp critically high"));
+
+        var plan = Phase7Planner.Compute(previous, next);
+
+        // Guard the arrange: ONLY ChangedAlarms is populated.
+        plan.ChangedAlarms.Count.ShouldBe(1);
+        plan.AddedAlarms.ShouldBeEmpty();
+        plan.RemovedAlarms.ShouldBeEmpty();
+
+        var outcome = applier.Apply(plan);
+
+        outcome.RebuildCalled.ShouldBeTrue();
+        outcome.ChangedNodes.ShouldBe(1);
+        sink.RebuildCalls.ShouldBe(1);
+    }
+
+    /// <summary>H1a guard — a deploy that ONLY changes a driver instance's config must NOT rebuild the
+    /// address space. Driver-instance changes route through DriverHostActor's spawn-plan in Runtime, not
+    /// the address-space topology, so <c>ChangedDrivers</c> is intentionally excluded from
+    /// <c>needsRebuild</c>. This pins the exclusion against accidental inclusion. (The pre-existing
+    /// <see cref="Driver_only_changes_do_not_trigger_address_space_rebuild"/> uses a hand-built plan;
+    /// this one drives the planner end-to-end.)</summary>
+    [Fact]
+    public void Changed_drivers_only_do_not_trigger_rebuild()
+    {
+        var sink = new RecordingSink();
+        var applier = new Phase7Applier(sink, NullLogger<Phase7Applier>.Instance);
+
+        var previous = CompositionWithDrivers(new DriverInstancePlan("d-1", "Modbus", "{\"v\":1}"));
+        var next = CompositionWithDrivers(new DriverInstancePlan("d-1", "Modbus", "{\"v\":2}"));
+
+        var plan = Phase7Planner.Compute(previous, next);
+
+        // Guard the arrange: ONLY ChangedDrivers is populated.
+        plan.ChangedDrivers.Count.ShouldBe(1);
+        plan.AddedDrivers.ShouldBeEmpty();
+        plan.RemovedDrivers.ShouldBeEmpty();
+        plan.ChangedEquipment.ShouldBeEmpty();
+        plan.ChangedAlarms.ShouldBeEmpty();
+        plan.ChangedEquipmentTags.ShouldBeEmpty();
+        plan.ChangedEquipmentVirtualTags.ShouldBeEmpty();
+
+        var outcome = applier.Apply(plan);
+
+        outcome.RebuildCalled.ShouldBeFalse();
+        outcome.ChangedNodes.ShouldBe(1); // driver change is still tallied, just not rebuild-forcing
+        sink.RebuildCalls.ShouldBe(0);
+    }
+
+    private static Phase7CompositionResult CompositionWithTags(params EquipmentTagPlan[] tags) =>
+        new(
+            Array.Empty<EquipmentNode>(), Array.Empty<DriverInstancePlan>(), Array.Empty<ScriptedAlarmPlan>())
+        {
+            EquipmentTags = tags,
+        };
+
+    private static Phase7CompositionResult CompositionWithVirtualTags(params EquipmentVirtualTagPlan[] vtags) =>
+        new(
+            Array.Empty<EquipmentNode>(), Array.Empty<DriverInstancePlan>(), Array.Empty<ScriptedAlarmPlan>())
+        {
+            EquipmentVirtualTags = vtags,
+        };
+
+    private static Phase7CompositionResult CompositionWithAlarms(params ScriptedAlarmPlan[] alarms) =>
+        // ScriptedAlarmPlans is the set the planner diffs into Added/Removed/ChangedAlarms.
+        new(
+            Array.Empty<EquipmentNode>(), Array.Empty<DriverInstancePlan>(), alarms);
+
+    private static Phase7CompositionResult CompositionWithDrivers(params DriverInstancePlan[] drivers) =>
+        new(
+            Array.Empty<EquipmentNode>(), drivers, Array.Empty<ScriptedAlarmPlan>());
+
     private static Phase7Plan EmptyPlan => new(
         Array.Empty<EquipmentNode>(), Array.Empty<EquipmentNode>(), Array.Empty<Phase7Plan.EquipmentDelta>(),
         Array.Empty<DriverInstancePlan>(), Array.Empty<DriverInstancePlan>(), Array.Empty<Phase7Plan.DriverDelta>(),