The general rule of thumb for BPs is to not feed them something bigger than the widest part of their body, so you're doing great with that, unfortunately we cant tell how big she is off of her pic on your profile, you should be good with rat pups following the general rule of thumb like you already stated. Most breeders try to stick to just rats, but BPs can be picky eaters. Personally i have a few that went off food and i tried a whole bunch of different things but in the end they just wanted something else to eat besides rats. I started to feed them Mice and they instantly went for it. This isnt always the case when they go off of food but a good tip. As far as switching it up on your own, i think it would be a decent idea just to try and give them something else to eat vs constantly eating the same thing for their whole life, But just an FYI if they do take the new prey they can go off food if you tried to switch back to rats after so keep that in mind that once you give them something else they can become stuck on that new prey and wont go back to the previous. Out of my 3 that i had to switch to mice, ive only been able to get one of them so far back onto rats and the other two wont even look in the rats direction when i try to feed them even though theyve eaten rats the whole time ive had them up until that point they went off food.