A long time ago I was doing something to my xbox 360 elite (case mod I think) and I saved my serial sticker or whatever that thing is under the faceplate. Is that worth anything? Like could someone put it on their Xbox to send it in to get repaired?
No it's not really worth anything. It would be almost impossible to put it back on how microsoft did, even if you tried, you'd be putting back on because you voided your warranty by opening the console, Microsoft could tell if you did that. If it's over two years old then it's useless.