Can't decide until housing assignments are out (after May 1)

Here's the ideal situation for me (assuming I got an offer from both College A and B):

College A has better academics ranking but requires live on campus without a guarantee for my room preference X.

College B has lower rankings but does not require living on campus, so I can find room type X wherever in the city.

The best case scenario is I accepted the offer from College A AND got my room type X. But since that isn't guaranteed, I'm not willing to risk not getting my room preference. So, ideally, if I ended up not getting my preference, I can still backup and go to College B.

But here's the problem, essentially, I won't have my decision until July, and double depositing is considered really bad. This is different from trying to negotiate financial aid ( collegevine.com/questions/14306/can-change-my-decision-after-may-1st ) since usually I can only apply for housing after I accepted (deposited) the offer.

I'm also aware that depending on the high school, they may send the final transcript to one school only. So far, online forums have told me to either deal with the risk or only apply to schools that do not require living on campus.

I know that I'm legally allowed to switch schools even after I accept their offer. In fact, it's common among freshmen that it's called summer melt. But confusingly, if I can't be holding multiple offers after May 1, then where can I possibly switch to in the summer?