Slightly improve error message in case of duplicate entity IDs (#45424)

homeassistant/components/config/entity_registry.py

@@ -102,7 +102,9 @@ async def websocket_update_entity(hass, connection, msg):
         if hass.states.get(msg["new_entity_id"]) is not None:
             connection.send_message(
                 websocket_api.error_message(
-                    msg["id"], "invalid_info", "Entity is already registered"
+                    msg["id"],
+                    "invalid_info",
+                    "Entity with this ID is already registered",
                 )
             )
             return

homeassistant/helpers/entity_registry.py

@@ -388,7 +388,7 @@ class EntityRegistry:
 
         if new_entity_id is not UNDEFINED and new_entity_id != old.entity_id:
             if self.async_is_registered(new_entity_id):
-                raise ValueError("Entity is already registered")
+                raise ValueError("Entity with this ID is already registered")
 
             if not valid_entity_id(new_entity_id):
                 raise ValueError("Invalid entity ID")