I think they'll be smart enough not to put in crashcode or malware, but they'll almost certainly set the mod up to deliberately fuck up any changes made by a mod they deem problematic, and then pretend that it's not a deliberate, artificial problem when confronted.
Starsector had the same thing, you had that one insane tranny who went all-out with borderline malware sticking out the most, but a bunch of other modders had stuff set up to fuck with the game more subtly if they detected any wrongthink mods running, such as locking you out of content, or deliberately overwriting parts of the other mod's content, etc. It'd probably be easier to do with Terraria honestly, since there's so many places where something could just go wrong entirely "coincidentally".