I hate Early Decision, and I believe it is entirely a strategy used to increase a school's yield and take what little control candidates have away from them.
However, I understand that it exists, and there are agreement terms, and you don't want to get in trouble. Until this thread, I was under the impression that reneging on an ED admit was actually somewhat common. I had a consultation with a consultant last year and she advised me to apply to Columbia Early Decision. Since my target schools were all in the midwest, I asked about what I should do if I ended up getting into Booth, for instance, and she told me I should eat my deposit at Columbia and go to Booth instead. I was surprised, but it gave me the impression that you can just do that.
Not to say she's a great source, since she was trying to improve her yield by getting me into an M7 I wasn't even targeting and potentially wasting 5k on a deposit there. However, I feel like a school doesn't (or at least shouldn't..) have any right at this point to demand further tuition from you. This is an interesting discussion.
Edit: Relevant post -
Will Early Decision Boost My Admissions Odds at Columbia GSB"This begs the question – what happens if you gain admission under Early Decision, pay the deposit, but later get into a school you prefer, like Harvard? At
MBA Admit.com, we have seen candidates simply choose to lose their deposit to Columbia and accept the school they prefer. We don’t comment on whether you should do this or not, but we can state factually that we have seen this done. For those candidates, they were willing to pay the deposit in exchange for getting a boost toward success in the Columbia admissions process and they were willing to lose the deposit if they got into another school that was their first choice. "