If they took that line, my lawyer would be taking the line that if the money part of the contract was locked in, it was too late for THEM to be making adjustments to the rules. Can't be changing the product (exhibition space) after it's already bought and paid for and non-refundable, can we? In fact, even if the money WERE refunded it might be worth pursuing them for breach, because the exhibitors lost the opportunity to make MORE money than the booth cost or they wouldn't have been buying it in the first place. I believe it's called the "benefit of the bargain". The show entered into the agreement with one set of provisions, then thinks they can unilaterally change the provisions after the fact, in such a way that it makes their performance less valuable to the other party, with no recourse?? BS, I say.
Serously! I mean, what other changes could they make on a whim at no cost to the promoters?