@new nickname 4 I have a live chat w/CS and let them know I'm getting ready to send back to do an exchange and to please make the notation on the order and/or my account that I'm exchanging.
I've done a couple of exchngs recently and they were seamless - no more s/h, no credit for the item sent back, no new charge for the exchanged item.
There's no reason why you should be charged more just because it was a tsv. They will/certainly should honor the same price.
I would notify them if I were you, and ask about the price too. You will be instructed to used their prepd label, and I would also place a big note inside that you're doing an exchange.