Frank,
They're going to enforce it wherever the law is being broken.
Worse part, it's not just going to affect people with headers, most stock thru transom exhaust will not pass either.
People at Rex Marine are working on mufflers that will lower the decibal readings without any loss of power...a tall order to fill but I'm glad they're doing the necessary R&D.
Too bad people just don't want to get involved to try to get the levels raised?