If I can, I try to keep it from biting with some tongs, but sometimes it is impossible. I've had a bite here and there but honestly, they are not a big deal!! Your snake is wearing armor plating (scales) and is a killing machine. If the snake is not constricting the rat and the rat is fighting the snake, just remove it. If the snake is hungry, it will kill the rat even if it does bite.
Aggressive rats only become a problem when they are left with a snake that is not hungry for too long. Eventually the rat turns on the snake and sometimes the snake will not defend itself.
Supervise your feedings and everything will go smoothly.