Kind of a shorter version of what Gannet said. There's the LAW, and then there's the dealers interpretation of the LAW. Since you've already installed headers and cats, you're playing with the possibility the dealer may deny warranty coverage on your car. Some dealers will let it slide, others will make you fight for it. I don't know of any custom tune a dealer could not detect if they looked for it. Also, if you've got a custom tune and take the car in for any maintenance that requires a reflash, goodbye custom tune. Bottom line I guess is, if you're going to mod your car, be prepared to duke it out with the dealer, unless they're really cool. Good luck.
