I don't know if there is a more right answer here, I know people feed their snakes two rodents consecutively all the time. But if it were me, I personally would choose to feed them 4-5 days apart instead of on the same day until you run out of what you have, then upgrade. Of course, BPs CAN be tricky to get to switch sometimes, though not always.

I am close to making a switch myself, my girl is on adult mice right now and I have two left in the freezer. The are just ever so slightly too small for her, she is ravenous and snappy after six days, not seven and they barely leave a bulge in her anymore. I plan on introducing her to rats in a couple weeks when the mice are gone and hope the transition is easy. She has been a really good feeder so far, so I have high hopes. But you never know!

Best of luck!