If it has only been out for a short amount of time you can re-freeze it. From your post I assume the rat started out as f/t? You can successfully re-freeze rats once, but after that it starts to get gross and you will want to throw it away. Did you thaw it in warm water? I highly doubt that you cooked the rat unless you boiled it or zapped it with high heat for a long time. Your BP is just being a BP, these snakes are finicky eaters at best. As long as your husbandry is correct, give the snake 3-4 days and try again. You will see on this forum tons of posts about problem feeders, and you will see a litany of responses giving advice on what to do. You can try any and all of these measures, but from what I have found, BPs with correct husbandry will eat just when they are good and ready.