I would not feed a snake a rat with lice.

Look, I breed my own rats because I want my snakes to have the healthiest food possible so why would I feed them something that has a parasite? Where did you get these rats with lice? I'd take them right back to the place you got them from and demand your money back. Or if you breed them yourself you really need to think twice about how you are treating your animals. They may be "just rats" but they're an extremely intelligent animal and they deserve to have a comfortable life even if they will be snake food eventually.