There is couple of things here first switching can take time and sometime and you might have to practice tough love if your BP has a good body weight. There are also BP that have nothing to do with a rat (I have one).

When you fed mice were they live?

If you do, try offering a live rat pup (same size than adult mouse), and if at some point you want to switch to P/K or F/T do it one step at the time, once your BP is switched to rats and ate successfully 3 to 4 times, try to switch to PK or F/T if that is what you want.

Also avoid stunned rats this is cruel and not necessary, and could also cause problems making the rat more aggressive if he wakes up.