With my guys, it's all about the heat of the rat, I switched my adopted 5 year old over to F/T a few months ago, he'll only take it if the rat is at least 85-90 degrees. I use a temp gun to make sure. I'm not sure about re freezing thawed out rats, but I have done it before, mine was only out for 30 minutes though. I tend to be overly cautious, and if my guys won't eat, I usually end up tossing the rat =/
Try giving him a few more days before you offer again? Maybe he'll be hungrier and not care as much.