diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagModal.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagModal.razor
index 2cd5c3b9..677656b9 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagModal.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagModal.razor
@@ -336,14 +336,12 @@
     private void OnGalaxyAddressPicked(string address)
     {
         _galaxyAddress = address;
-        // A fresh {FullName} blob would drop any tag-level historize the operator already set on this
-        // edit; re-merge it so re-picking a Galaxy address never silently clears "Historize this tag".
-        var config = TagHistorizeConfig.Set(
-            JsonSerializer.Serialize(new { FullName = address }),
-            _historizeState.IsHistorized,
-            _historizeState.HistorianTagname);
-        // Re-merge any array intent for the same reason — a fresh {FullName} blob would otherwise drop it.
-        config = TagArrayConfig.Set(config, _arrayState.IsArray, _arrayState.ArrayLength);
+        // Re-picking a Galaxy address owns ONLY the address-derived FullName key — apply it over the EXISTING
+        // TagConfig so every other user-edited field survives verbatim. This preserves a hand-authored `alarm`
+        // object (FB-4: a re-pick must never clobber edited alarm fields) as well as the root history/array
+        // intent and any driver/unknown keys. TagConfigJson.SetFullName uses the same preserve-unknown idiom
+        // as the historize/array merge seams.
+        var config = TagConfigJson.SetFullName(_form.TagConfig, address);
         _form.TagConfig = _galaxyPickedIsAlarm
             ? NativeAlarmModel.SeedDefaultAlarm(config)
             : config;
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs
index 8f317a4c..136fcc34 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs
@@ -43,4 +43,19 @@ public static class TagConfigJson
         if (value is null) { o.Remove(name); return; }
         o[name] = JsonValue.Create(value is Enum e ? e.ToString() : value);
     }
+
+    /// <summary>
+    /// Merges a freshly-picked Galaxy reference (<c>tag_name.AttributeName</c>) into <paramref name="json"/>
+    /// by setting ONLY the canonical PascalCase <c>FullName</c> key — every other key is preserved verbatim.
+    /// This is the Galaxy address re-pick seam: re-picking an address must update the bound attribute WITHOUT
+    /// discarding fields the operator already edited independently of the address — ESPECIALLY a hand-authored
+    /// <c>alarm</c> object (and root history/array intent, scaling, etc.). Null/blank/malformed input starts
+    /// from a bare <c>{"FullName":...}</c> object.
+    /// </summary>
+    public static string SetFullName(string? json, string fullName)
+    {
+        var o = ParseOrNew(json);
+        o["FullName"] = JsonValue.Create(fullName);
+        return Serialize(o);
+    }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/GalaxyAddressRepickMergeTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/GalaxyAddressRepickMergeTests.cs
new file mode 100644
index 00000000..109456f5
--- /dev/null
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/GalaxyAddressRepickMergeTests.cs
@@ -0,0 +1,84 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Uns;
+
+/// <summary>
+/// Unit tests for <see cref="TagConfigJson.SetFullName"/> — the pure merge helper the TagModal's Galaxy
+/// address-picked handler uses to apply a freshly-picked <c>tag_name.AttributeName</c> reference. Re-picking
+/// a Galaxy address must update ONLY the address-derived <c>FullName</c> key and carry every other
+/// user-edited field over verbatim — ESPECIALLY a manually-authored <c>alarm</c> object (FB-4 / B2). The
+/// previous handler rebuilt the config from a bare <c>{"FullName":...}</c> blob, silently dropping the alarm.
+/// </summary>
+public sealed class GalaxyAddressRepickMergeTests
+{
+    [Fact]
+    public void Repick_preserves_an_already_edited_alarm_object()
+    {
+        // The operator authored an alarm, then re-picks the bound attribute to fix a typo.
+        const string current =
+            """{"FullName":"Pump_001.OldAttr","alarm":{"alarmType":"LimitAlarm","severity":250,"historizeToAveva":false}}""";
+
+        var merged = TagConfigJson.SetFullName(current, "Pump_001.NewAttr");
+
+        // The new address is applied...
+        var fullName = ReadFullName(merged);
+        fullName.ShouldBe("Pump_001.NewAttr");
+        // ...and the hand-edited alarm survives the re-pick intact.
+        var alarm = NativeAlarmModel.FromJson(merged);
+        alarm.IsAlarm.ShouldBeTrue();
+        alarm.AlarmType.ShouldBe("LimitAlarm");
+        alarm.Severity.ShouldBe(250);
+        alarm.HistorizeToAveva.ShouldBe(false);
+    }
+
+    [Fact]
+    public void Repick_with_no_alarm_just_sets_the_address()
+    {
+        var merged = TagConfigJson.SetFullName("""{"FullName":"Pump_001.OldAttr"}""", "Pump_001.NewAttr");
+
+        ReadFullName(merged).ShouldBe("Pump_001.NewAttr");
+        NativeAlarmModel.FromJson(merged).IsAlarm.ShouldBeFalse();
+    }
+
+    [Fact]
+    public void Repick_preserves_other_user_edited_non_address_fields()
+    {
+        // History intent + an array shape + an arbitrary scaling key the operator set independently of the
+        // address — all must survive a re-pick that only owns FullName.
+        const string current =
+            """{"FullName":"Pump_001.OldAttr","isHistorized":true,"historianTagname":"Line3_Temp","isArray":true,"arrayLength":8,"scale":0.1}""";
+
+        var merged = TagConfigJson.SetFullName(current, "Pump_001.NewAttr");
+
+        ReadFullName(merged).ShouldBe("Pump_001.NewAttr");
+
+        var hist = TagHistorizeConfig.Read(merged);
+        hist.IsHistorized.ShouldBeTrue();
+        hist.HistorianTagname.ShouldBe("Line3_Temp");
+
+        var arr = TagArrayConfig.Read(merged);
+        arr.IsArray.ShouldBeTrue();
+        arr.ArrayLength.ShouldBe(8u);
+
+        merged.ShouldContain("\"scale\":0.1");
+    }
+
+    [Fact]
+    public void Set_on_empty_or_malformed_input_starts_from_a_bare_FullName_object()
+    {
+        var merged = TagConfigJson.SetFullName("not json", "Pump_001.NewAttr");
+
+        ReadFullName(merged).ShouldBe("Pump_001.NewAttr");
+        merged.ShouldStartWith("{");
+        merged.ShouldEndWith("}");
+    }
+
+    // Mirror of TagModal.ReadFullName — extracts FullName from a Galaxy TagConfig blob.
+    private static string ReadFullName(string json)
+    {
+        using var doc = System.Text.Json.JsonDocument.Parse(json);
+        return doc.RootElement.TryGetProperty("FullName", out var fn) ? fn.GetString() ?? "" : "";
+    }
+}