I think Dtrimpi87 was just stating what others are thinking in terms of you buying a car and then you complain of its cosmetic state after you took it home.
In regards to warranty it is very simple and you can look it up under Magnuson-Moss Warranty act...Wikipedi below, SEMA has a better listing if I remember correctly.
Bottom line is that unless the part you installed directly effects or causes the part you are trying to warranty to fail they cannot deny the warranty. IE: a 1LE suspension, NPP Exhaust nor the ZL1 shifter are not going to cause your ECU to fail or your motor to drop a valve.
If the dealership tries to deny a claim for warranty based on an aftermarket install you insist for this denial to be in writing (they wont do it). If they do not have proof that your install or component has a direct correlation to the failed part they cannot deny the claim.
NOWWWWW. If you put a ZL1 shifter in your car and your trans starts grinding they can of course try to link the two and can stating incompatibility not allowing the the trans to fully engage in the gear causing the teeth to grind or wear...ect. Those types of claims are hard to fight as a consumer. But if the A/C stops working there is no direct link unless during your swaybar install you damage an a/c line (you get the point)
It is 100% case by case.....but there is no such thing as "VOIDING A WARRANTY" across the board unless the car has been hit and rebuilt or has been in a flood....everything else can be warrantied period!..Dealerships cannot VOID or black ball a car for a few mods....