If you have a special license you can get around it. there are states that have like a show vehicle class you can license you car under. it alows you to break some of the laws.
in all honesty I have never had a legal car for very long and have been pulled over so many times I can not count and have never had a cop look for cats. So are you basing this on first hand experience or just assuming that cops look for cats?
ahhhh....I love living in the country. I have no emisions rules to go by here. Could blow all the smoke you wanted and there would be nothing the cops could do about it.