I think the White House made a brilliant move. They're letting Acosta hang himself.
They didn't try to fight it out in court. Rather, they formally codified the rules and issued a neutrally-worded statement spelling out what had generally been the "understood" rules all along. I'm betting they will rigidly enforce them, at least for a while. Acosta will play nice for a week, maybe two. Then, when he thinks they've gone on to other things, he'll revert to his usual jackassery. That's when they have him dead to rights and CNN can't pull another "find a judge who agrees with us" stunt.
Brad