Thanks! As far as I know, werewolves autonomously biting sims to turn them into werewolves is actually in the vanilla game - I've had Greg do a walkby in a random residential neighborhood on the full moon and attack one of my sims before. If you lose the fight, there's a very high chance your sim gets infected with werebies. There's also a chance for other werewolves to trigger this, it's just much lower.
If Greg's not showing up, you may need to turn the full moon to always be on in settings.