Yeah, they weren't "banning racecar conversions" they were banning racecars that have been modified from their EPA certificate... like engine swaps and exhaust/cam/intake/ecu/carburetion configuration changes.
Don't worry, they promised to selectively enforce it only on street-driven cars...
The change is in the past they considered a competition vehicle based on use, not a case of "ever having been in a certified condition."