Not really "no go", but a "do you really need this?"
If you must, within the client tag change script, include a check for the specific client's MAC ID, or something else unique, and only perform the navigation if it matches. That'll keep your designer from firing on it while in preview mode.
You can perform that MAC ID check once in a client startup event and save the result to a client tag (if you have other things that should be limited to that one client). See this topic for a method: