If any of those snakes you're trying to switch are females, and you're breeding them, the best time to try to switch them is right after they lay a clutch of eggs--they are hungry and will take most anything you offer. I'm hoping to use this trick to get my het albino female on f/t . . . if she ever gets to breeding size (the picky girl LOL). Right now she will only take pre-killed (but hey, at least it's not live), and she is more stubborn than me, especially since I'm trying to get her up to weight for breeding. I tried f/t for a while and she outlasted me. But I'm hoping the "right after egg lay" thing will do the trick if she ever gets there.