Rats vs Mice

My 3 new girls have been eating live weaner rats, but none of the pet stores anywhere near me have rats that size (I've got baby rats born last week- should be right size in another couple of weeks).
Here's the question- if I try to feed them the appropriate sized mouse instead (until the ones I bred are to size), is that likely to be okay, or will swithching from rats to mice then back to rats again screw them up?

BPs can imprint on food, so it is possible that it will cause a problem. It is also possible that they will refuse the mice if they are imprinted on rats.

However, I have read lots of posts from people that say their snakes switch back & forth with no problems.

One thing you could consider if you are concerned about it is to skip a feeding or give them a small meal even though your rats aren't up to size yet.