I did this recently. They would only exchange for in stock items and would not issue me store credit.
Exactly what I experienced. I returned an item bought in France to a US boutique (although years back at this point), and the credit I received was for that day only and in that boutique. @stillfabulous, it may be best to call ahead to see if any of the items you want instead are actually in stock, or at least have a number of items in mind to request when you go in to exchange.