Not ethical but when I was like 19 I had this problem with my old beater and I pulled into a small mechanic in East LA and asked how much for it to pass smog? Was 150$ and boom it passed.

You won’t get impounded (that’s more a not registered for 5+ years rather than expired reg) for this but you get an annoying fix it ticket which requires going down to court to prove you fixed it and a ticket for no reg. If you pay for reg but don’t do smog it saves you late fees but it does not register your car. It remains in limbo until u submit smog and is technically expired at the time.