Well, the first paragraph says that it's allowed to break the rules if both parties have agreed to it and it's safe.
The rules are necessary though. The rule to have flash guards on your muskets has been in the rulebook since at least a decade and there were still groups that didn't use them as late as last year. My favorite group *cough*, the Douaniers Imperiale, suddenly decided to get them after someone had been injured (always takes a casualty to get some change) and the NAN didn't do shit about the fact they hadn't used them for years. It makes it rather hard to keep to the rules if you know that people who break them get away with it.
That being said, apart from the Rules-mania, the NAN is a great organization and we're truly blessed with it. They represent all the Napoleonic re-enactors here, and doing a damn fine job at it, and that way we managed, and will manage, to get some nice events.
