Do the mock booking as suggested, and they should be able to reprice without cancelling. Just make sure they send you the invoice and make sure it’s refundable before you say ok and get off the phone with them. When repricing, they usually forget to make it refundable, at least the last few times I repriced. And the price for refundable deposits could changes quite a bit from day to day for some reason, if offered. I’ve also upgraded (actually was $150 less to move up two categories in COVID times) and it didn’t change the reservation. But if you can wait for the refund (about a week or two), like firefly says, no harm to book and cancel.