Power transmission is not through your bike shifter setup unless you build it that way.
Sick Bike Parts and others have a set-up like that but it's extra and a lot more than a motor kit usually. The front sprocket gets a freewheeling gear so you can still pedal with the engine off so it is still a motorized bike.
Yes, the do have a manual clutch but that criteria is ignored by the vast majority of law enforcement. An automatic clutch is also available but you should also add a pull starter.
I can tell you I have never heard of anybody being hassled for having a clutch. Idaho law says the same thing, I swear that most of the states photocopied the same set of laws and just had the Government rubber stamp the approval. Occasionally you have a state of "original thinkers" who want to curb us outlaws. I'd bet the bastiches are Insurance salesmen, too
Or money grubbers that think to balance bankrupt state budgets on the backs of motorbikers. HAHAHAH good luck with that.