The thing to keep in mind here is that yes, J-Rod is right, if you really want to make sure you have no warranty problems, leave the car stock. Having a modified SRT-4, I know all about the world of trying to get warranty service with a modified car. The fact is, any dealer can refuse warranty service for any reason, EVEN IF YOUR CAR IS STOCK. Mitsubishi dealers especially are notorious for googling through auto-x results, and blacklisting their owners for denial of any future warranty claims. If you bring your car to the dealer with an aftermarket intake and bov, and the muffler fell off on the highway, they don't have to honor that.
Now yes, we have the Magnuson-Moss warranty act to help us out, that's a huge benefit. But like anything else, you can't physically make them follow it, they're free to deny your claim for any reason, its up to you to convince them to honor it. Most dealerships will work with you if you simply ask how your installed part voids the warranty. Or if the failure or defect is related to suspension, braking, or safety equipment, they will almost always fix it, since they don't want to deal with a major lawsuit should you become injured or killed in a wreck thanks to a mechanical failure on their car that they failed to fix. Yet they can deny powertrain claims all they want, even if you bring up the ol' M-M. You can print it out and try to explain to the service manager, and often he'll have no choice. But if they still won't honor your claim, you don't have much choice other than to either go somewhere else, or get a lawyer involved.
This is simply the reality of things, the dealer knows they can just flat deny you if they want, and the costs of you getting a lawyer involved are almost always gonna cost more than the repair work. They know this, and will often take advantage of that fact. Granted, that can hurt their reputation among other enthusiast owners of your same car, but unfortunately, they know it will have little if any affect on their overall sales.
In summary, the Magnuson-Moss Act does protect us to a degree, but by no means does it guarantee that you will be able to get your car fixed for free after you have done any mods or competition at all. It means that you have something to use in court to make them honor your claim, but rarely is it gonna be worth going to court over. So, if I were you, I'd get to know the service manager, and talk to him a bit and see how they're gonna be. Mention the act if you want, but try to get some statement or at least the general feeling that you will be treated fairly regarding possible warranty claims before you do anything to the car. If not, tell them this is unacceptable and you will be seeing another dealer for all your scheduled service, and even the initial sale if you haven't bought the car yet. But find out before, don't find yourself having to fight the dealer in court for something that won't be worth it.
Oh, and remember, stealership or not, they're still not your pit crew.