Do not use your Preview Environment for any "ALPHA" or "BETA" testing. Preview is purely meant for development and developer testing.

The best scenario for running ANY kind of alpha or beta is to create a specific Alpha/Beta credential, publish a snapshot to live, and have players connect to that. When the alpha/beta is over, they can delete or modify their connection credential to disallow the player to connect any more, but still retain player documents on the live service.