Is it illegal to change the firmware in my xbox 360 DVD ROM, if I will never go on line, and will only play games that I have bought?

The games are ridiculously expensive, about $60. I want to buy games at retail and protect them from damage. I want to produce a playable copy, and archive the store bought disk, so I don’t damage it. This will allow me to play my copy, and if it is scratched, no real loss. I will never play on line, and will never give or loan any copies to any one. Is this legal?