Through lots of reading and research upon here. It seems BP's are quite known for being finicky eaters. Like what most people will suggest, double check your husbandry. Temps, humidity, etc. Could be stressed, could be just that time of the season where they go off feed for a bit. Just continue to offer him food as you normally do with his feeding schedule. And eventually he'll break that cycle and get back on eating.

Switching from mice to rats tend to vary from snake to snake. I was very fortunate that my BP started off with Rats. And he's currently on rat pups, until he get's bigger and older. Good luck, keep us updated