This probably isn't a very helpful post, but...
Are you in a city or out in the sticks? Because I live a stone's throw from the NH border in a rural area and the NH cops have never harassed me or anyone for loud exhaust that I have seen. Maybe that's a down south thing?
I have run straight shorty drag pipes (very very
loud) on a bike in NH with zero problems, for instance. But maybe I just got lucky? Honestly don't know.
I'm kind of shocked to hear about such a restriction on our beloved Live Free Or Die neighbors...you guys normally have the 'cool' laws.