I think you are totally right in bringing the millennium rules into your series!!!The NSPL is trying to encourage teams to develop from KotH level right through to Millennium level. Hence the Millennium rules.
Do we not have a responsibility to enforce these rules so teams get used to them before moving on to International play?
But I do firmly believe that the rule is intended for more extreme stuff than "f*ck those guys" backplates etc.... I honestly believe we are talking extreme things like for instance nazi-logos or stuff in that "league"! So all you people can probably keep your swearwords hehe.....
And yeah - I doubt any ref will be "anal" about the mentioned stuff - at least I have never heard of or experienced any such in the millenniums yet!
The rules are there to be followed - but actually in this matter it is strictly up to the ref to decide wether or not a sticker or a logo or jersey or whatever is too offensive to wear or not!