This sounds like an ideal use case for electric cutouts - add a new restrictive muffler that the cutouts direct flow through. Then when you "need" it louder, open the cutouts, they bypass the new mufflers and go straight to the Flowmasters.
I've lived in neighborhoods where idiots on straight-piped Harleys go roaring down the road at 5am, or diesel trucks go rolling coal for fun, or where kids in Hondas rip around with fart can exhausts. Nobody likes that guy, don't be that guy.
1969 Cougar | 1997 M3-5.0