The standard statement for denying warranty or insurance cover is if they can show the modification caused the claim. For grilles, that might possibly (possibly!) be if the engine is overheating or the aircon not working. But it's the small dog barking loudly; both know that if the lawyers got involved there would be no winners, especially once the denial got amplified on social media and they'd lose easily twice as much in future business.
As Patt illustrates, it's a bark with little bite.