I can say that as the performance car manager of Hechler Chevrolet (Hechler Motor Co of ZL1 fame) druing the mid '90's that we didn't care. The zone reps would come by the dealership and look around, but I never saw them deny warranty claims. Hell, we even had one look at a Z28 with slicks on it, and enough rubber on the quarters to make a new set of tires get warrantied for a broken 6spd. Maybe there were some over zealous zone reps, but from what I saw/heard as long as the dealership didn't get flagrant with it, no big deal. Just my experience anyway.