Yes, you can modify it as long as you return it to stock when the lease is up or if they buy it back from you with the modded parts. Every dealer has a different policy, obviously your best bet is to call the dealership. The only way a modified part can void warranty is if it is the direct cause of a malfunction, IE hydrolocking when you have a CAI. But if your wheel bearings go, they cannot refuse to cover it under warranty because you have headers. Get it?