Ive had mine modified since I got my car in 2002. I got stopped in Rochester two summers ago for talking on my cellphone and the sheriff mentioned it but never really said to fix it.
I got actually pulled over at 6am last summer driving back to Buffalo from Rochester (Fairport) and passed a town cop in the left turn lane and he pulled into traffic to pull me over because my exhaust was modified. Not even reving or running in a low gear at high rpms. Just normal driving so it really just depends on if the cop wants to be a dick.