uhm, retroactive rules? There is a good reason why virtually every law system explicitly forbids that.
No law system gives any mention to rules in regard to a fan forum, except in some cases that revolve around actual threats. This is not property, a corporation, a job site etc. but even in those cases rules can be made retroactively in certain circumstances. So actually every law system may forbid such things in the proper circumstances or context, if you will but not explicitly.