I bought a used iphone 4 but the back has scratches on it and the back camera is really scratched, and the bottom metal sides are all scratched too. I'm planning on buying a new metal casing, and original backcover or maybe a metal one. I checked and the warranty is gone so, does it matter if I change the casings and back? I just want to make sure apple doesnt refuse me service if I take it in for something, even if I have to pay for it.