You can create "local" rules to new threads that you create that would apply to that thread only and are in addition to the forum rules.
Self moderated threads were introduced (march 2013 they were introduced I believe). Which effectively allows you to decide your own rules. Local rules may still apply to Scam Accusations, Important Announcements, and Auctions as self moderated threads may not be created in those sections to my knowledge. So, they might be valid everywhere, but most people would just make a self moderated thread instead except where it isn't possible.
This probably eliminates the rule stated. I'm not sure where I've read it but I think that local rules are no longer enforced by moderators.