Technically ANY alteration to the vehicle can void the warranty. However the manufacture is not interested in getting into a hair splitting contest with its customers. If you changed the tail lights about the only reason the dealership would say we are not going to pay to fix your problem is if they found the whole wiring harness melted from the dash straight to your nice new tail lights. A highly unlikely event I admit. If warranties were canceled on all vehicles with alterations there would be few vehicles on the road with one.
