there is no real answer to this and clearly you place a lot more faith in dealers/warranties than i do and we can go around forever because it's all hypothetical. if you go talk to some evo owners on the other hand they'll laugh at you if you mention warranty if it is any sort of real problem that needs to be addressed
it's pretty easy to show that a power enhancing device caused a drivetrain part to fail. so what you're saying is true, aftermarket parts are not automatic grounds for warranty denial. you are however opening yourself up to an easy out for the dealer to take. if they were voiding your warranty on your stereo because you put on an intake that's another story but modifications to anything in the powertrain to increase performance can cause parts and seals along the way to be exposed to conditions outside of their initial design and thus the warranty on the related part that failed is voidthat isn't correct. no matter what the part does, if it offers a quantitative performance increase in some manner, increases efficiency, enhances appearance, whatever...you are allowed to add that part, provided that it does not directly contribute to the basis of a warranty claim. if the part is found to be the direct cause of a problem, then that problem is not mazda's responsibility, however, the mere presence of an aftermarket performance item is by no means, 100% NOT VALID GROUNDS FOR AN AUTOMATICALLY voided warranty. If you read the warranty information for your car, you will see that it summarizes this exact notion, something to the effect of "adding aftermarket devices that alter engine ignition timing, fuel delivery or boost pressure may lead to serious engine damage and MAY VOID YOUR WARRANTY". i have yet to find conclusive information in the Mazda warranty that dictates an automatic denial based on the presense of aftermarket equipment...
as far as i know the entity that your warranty is through (mazda usa) is a separate legal body than the entity that made the intake (mazdaspeed, of which dealers are distributors) and the entity that sold it (the dealer). the letter is irrelevant. my point was that just because it came from a seemingly mazda entity does not mean that it is endorsed by the company that holds your warranty (mazda usa) but instead the exact same as if you bought a different brandi think this one is a misinterpretation of semantics on your end. mazda dealerships offer(ed) the intake, which was designed through a performance division for installation on their vehicles. From what i've seen, it's not SOP to require owner agreement to some sort of warranty addendum or disclaimer based solely on the installation of that part. There may be warnings about a correlation between it and potential issues, however, there is no legal addendum inferred. Maybe some dealerships instituted that, or there is some sort of card and accompanying literature that dictates some sort of warning, however, again, the fact that one can add that intake and forgo coverage, or at that one and not another style and forgo coverage is ridiculous. That is said without regard to the original fact that you can indeed add a part without automatic issue.
as far as i know a mazda dealer can NEVER void your warranty. they can deny warranty work and they may tell you that it is void but only an employee of Mazda USA can actually void your warranty as the dealership has no right to do so based on the fact that they are not an entity in the contract. they file your warranty claim just like a body shop files your insurance claim after an accident, just mazda gets billed instead of the insurance company. the body shop can't cancel your insurance and the dealer can't void your warranty. either entity (body shop or dealer), however, can bring suspect acts to the attention of the paying party (mazda or ins co)possibly, meaning this type of mistreatment might occur with that thinking abound, but since the warranty isn't through them (it's ideally backed by Mazda USA), they they can't effectively void it. And moreover, they can't automatically do it based on what we've talked about (merely adding a part).