I was in a sort of situation like this. I bought a 17" iMac (remember those) and decided that I wanted a 20" instead. I figgered they would waive the restocking fee since I was upgrading. Boy was I wrong. Apple store manager was a major AH. Need less to say, after the jerkiness of the manager, it became a return rather than an exchange- and, yes, they did get me for the restock.
So I called up AMEX. AMEX reversed the FULL charge when I complained, so Apple then lost the sale AND the restock fee.
So, my lesson to you is, call up the CC company. Depending on the terms (and these do vary), and what your CC company can do. AMEX is pretty good about this- they covered part of that 200 discount Apple did on the iPhone, and they do go to bat for you in instances like this.