I've questioned that myself. Is yours considered a "production" class?
I don't have an answer, but I can say that some of the variables I've run into with the Midget, being a production based class, and factory production run based requirements, have been -
A switch from 2 to 3 windshield wipers
Split rear bumper to solid one-piece rear bumper
Side marker light location
A one-year production change (1970) from squared off real wheel openings to arched rear wheel openings - and then back to squared off openings for 1971 - God only knows why
A factory switch from a flat-faced grill to a recessed grill then off to federalized "rubber bumpers".
I chose not to fight any of it and stuck with the original bad-aero grill opening, squared-off wheel arches and split bumpers.
At the end of the day, if you're in a production class, I suspect that the worst case scenario if you change out the grill is that you may have to have the car re-registered as an '83 with a new SCTA number and inspection.
I'd make a phone call - SCTA-BNI may not really care, but there are always those who do . . .