cleanup admin code

src/registrar/admin.py

@@ -2009,18 +2009,17 @@ def _handle_status_change(self, request, obj, original_obj):
 
             # If the status is not mapped properly, saving could cause
             # weird issues down the line. Instead, we should block this.
+            # NEEDS A UNIT TEST
             should_proceed = False
-            return should_proceed
-
-        request_is_not_approved = obj.status != models.DomainRequest.DomainRequestStatus.APPROVED
-        if request_is_not_approved and not obj.domain_is_not_active():
-            # If an admin tried to set an approved domain request to
-            # another status and the related domain is already
-            # active, shortcut the action and throw a friendly
-            # error message. This action would still not go through
-            # shortcut or not as the rules are duplicated on the model,
-            # but the error would be an ugly Django error screen.
-            error_message = "This action is not permitted. The domain is already active."
+            return (obj, should_proceed)
+
+        request_is_not_approved = original_obj.status != models.DomainRequest.DomainRequestStatus.APPROVED
+        if request_is_not_approved and Domain.objects.filter(name=original_obj.requested_domain.name).exists():
+            # REDUNDANT CHECK:
+            # This action (approving a request when the domain is active)
+            # would still not go through check or not as the rules are
+            # duplicated in the model and the error is raised from the model.
+            error_message = FSMDomainRequestError.get_error_message(FSMErrorCodes.APPROVE_DOMAIN_IN_USE)
         elif obj.status == models.DomainRequest.DomainRequestStatus.REJECTED and not obj.rejection_reason:
             # This condition should never be triggered.
             # The opposite of this condition is acceptable (rejected -> other status and rejection_reason)