I have done it a few times with my BP because I had a surplus of fuzzies. I've also done it when I was jipped on the size of my mice. I have never had an issue with it, and the snake seems just as content and comfortable with it as ever. Since they're smaller than what the snake is used to taking there shouldn't be negative effects regarding tissue lining, etc as the snake is not having to work the mouse nearly as hard as it does a rat to get it down.

Just my $.02.