Your trike should qualify for a state issued VIN, being it is powered by a car type engine & is probably hand made.
To get DMV "blessing" on it you would have to have paperwork showing where the parts came from. Typically they want a title or bill of sale depending on the year, for the frame. They also want the same for the engine/drivetrain components.
NH doesn't currently recognize "trike" as a body type for registration purposes, so having the DMV inspection is really not necessary UNLESS you get stopped driving it and the officer doesn't believe it is truly a "Honda" motorcycle.
Next time the registration is due you could go to the town hall & request the agent to get the registration to show # of cylinders as 8.
Other than that, why bother doing anything if you're getting by in registering it as a Honda motorcycle?
Sorry for Hijacking your thread -JackieJack