Yeah, but Giambi signed there as a free agent. He went there voluntarily knowing the rules. As I noted earlier, that's a bit different from being traded involuntarily. Say the Nationals traded Werth to the Yankees, for example, and he then refused to cut his hair. What kind of discipline, if any, could they impose, short of benching him (in which case he'd still be paid) or trading him again?
That's one reason why I asked whether the standard contract has some sort of provision requiring players to obey these kinds of team rules.