In GWD we provide a way to remove the association in the file that has been published to Studio before.
If you publish a file to Studio and then you click on the arrow icon next to the the Publish button to open the publish options, you should see a 'lock' icon next to Publish to Studio. You can click on it to remove the association and you should be able to enter new creative info. Can you try that and see if it works you?
Emily (GWD Team)