I've been looking, and so far I've found two mods that seem to do the same thing, one where the savage interaction is modified to be fun and another where a sim will "scuffle" with another without losing rel, both spreading lycanthropy. The savage interaction isn't available when both sims are werewolves, and the mod was made to not have them fight either. According to the comments, they'll just stare at each other before the interaction drops.

Both of those are cool and I can myself using them depending on what I would want to occur, but I want play fighting between two werewolves that hopefully would increase rel, if there's a mod like that.

I wouldn't mind a mod that allows play fighting between all sims.