I found it easier to convert hatchlings or under 100 grams. My older bps never took f/t for the exception of one male pinstripe that was on a hunger strike.
I let the rodents thaw out in fridge over night. I then place them on rack so they get to room temperture. I hit them on the head with a blow dryer right before I offer to snakes. One of my female mojaves likes them extra hot while some of them like them at room temp.
I always start with rat pups and if they refuse a few times i offer small mice.
It takes time. Good luck