At the risk of being seen as encouraging people to break the law, how would the EPA know if I went out and built 3 custom bikes for myself in the next few years? And I’m also unsure of what they would do for enforcement. There is an importer of Chinese built motor scooters who went through EPA certification only to have their EPA labels forged by a competitor. It was reported a while back last I heard, there had been no action taken at all.

The EPA rules are probably mostly written to stop companies from cranking out “custom” motorcycles without any emissions certification.

Your mention of “rebuilding” an old bike has merit, however I think the same could be done even with a newer bike. Every state has its own rules about what must be retained to be considered the same bike, but I bet in several states you could build a sport bike powered chopper with a unique frame and be just fine as long as you meet the requirements for turn signals, mirrors, etc.