i posted some info almost a year ago that was stickied but not anymore. well, aftermarket parts must be PROVEN to cause the damage to the warrantied part before you can be denied coverage. like if you install something that alters the emissions (no2, sc, Turbo, no catalytic converter, etc..) and causes damage then you can be denied emissions warranty. here's more info:
sema.org [
sema.org]