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A guy I work with has extensively modified his pulley, air intake, and other drive parts and he's still covered. I think one you start messing with the ECU or other core systems you're out of bounds, but stuff like driving lights, parcel shelfs and all cosmetic changes should be good. If you plan to put on a custom exhaust or do a 19% pulley or something, though, I'd check with your dealer on warranty status.