> "Anyone modifying a certified motor vehicle or motor vehicle engine for any reason is subject to the tampering and defeat device prohibitions of this section

> "Anyone modifying a certified motor vehicle or motor vehicle engine for any reason is subject to the tampering and defeat device prohibitions of this section and 42 USC 7522(a)(3)." IANAL, but it reads to me like you wouldn't be able to do that on one of these cars. The manufacturer could stop offering the muffler and you wouldn't be able to use a third party replacement whether it substantially changes the performance of the vehicle or not.