I like to put them in the refrigerator overnight or put them in a plastic bag immersed in hot water. After that I warm them up with a hair dryer. A tip for somewhat stubborn feeders is to blow the hair dryer over the rat and towards the cage so that the smell of the prey fills their enclosure. After doing this, my boy comes flying out of the tub looking for his food.

As for refreezing, in general it is not a good idea, because the animal decomposes rather quickly. The one time I tried to refreeze, the rats body cavity burst open and its guts went flying everywhere!

Hope this helps!
Benek