Identification of Existing Name
If you try to name another element with a used name, an alert shows in the bottom of the diagram editor. You can let the things as they are and do nothing - just ignore the alert or you can even close it to not disturb you. However, if you added a second instance of an existing object in your project there is an interesting option which this pane offers you - you can link the new element with the existing object. Click on the button with the name of the object and the model will be attached to the new element.