It will entirely depend on him if he switches back to f/t easily. Some do, some are a pain in the bum. As for refreezing, some people say you can refreeze once. I would not suggest refreezing if it was left in over night, but if you only have it thawed for a feeding attempt then it might be alright.

Also, I would call the pet store ahead of time and make sure they have live before making the trek. Some stores only sell f/t, and even those that ccarry live can run out some days.