At least in California, it would be a very rare thing for a policemen to cite someone for a smog violation. Pretty much it is a matter between you and the DMV if you fail a smog test for modification. The only reason for a smog test is to either get it registered here or to renew your registration here. If it fails, you don't get it registered. You either get it to comply or you take it out of California or you park it.
Policemen don't even study smog laws. They have other things to keep them busy.
