Number 5 is our Number 134.
You're missing a vital distinction, though.
Rules 1 through 4 list what is expected of you, the TFL Member.
Rule 5 isn't really a rule per se, as it it's not something that posters are either to do, or are not to do. There are certain actions/postings/ideas etc. that may not be covered adequately by rules 1 through 4; rule 5 says staff will deal with those situations when we come to them.
For example, nowhere in rules 1 through 4 does it say not to describe in detail how to convert a semi-auto handgun into full-auto.
Rule 5 would apply, as such an activity would fall afoul of Federal law, and we don't do how to break the law here.