If they where dicks and scanned the ECM calibration, they could possibly voided the warranty. But they would still have to sent the calibration values off to GM for validation before the warranty was void.
I had to send off calibrations for GM because we had a customer bragging to the tech about the mods he had and that he had to get the ECM "tuned." I took the pictures of the calibration and sent them off..... GM got back and said "He just had the tire size changes, go ahead with the repairs." The guy had different size wheels on it but also had ported heads, a smaller pulley, aftermarket header and exhaust, and an intake and it we still fixed the coolant leak (on the back of the engine) under warranty.
Your dealer has to prove that the mods caused direct failure of the parts. If they say no...Call Chevy customer service and CAC case started (Customer assistance center) ...that will get a fire under the manager's feet. It probably a common failure too...so then they cannot dispute your mods had anything to do with it.