In the World Wide Web you can find back covers, displays and more spares for your handset without problems. So you can repair your phone or change its look. However, is this legal? Do you lose your warranty? I’ve talked with a friend working at a local Nokia Service Center about this.
If you bought a new backcover, for example for your 5800 XpressMusic, you can change it without fear. Also Xpress-on covers can be changed without losing the warranty. However, as soon as you touch the screws you’re losing your warranty. Screws in Nokia handsets aren’t standard and you need a TORX5 or 6 spanner. You cannot buy it in your local store but you get it in the internet without problems.
Hot-Wire is offering this spanner for about 10€. I would not recommend repairing your brand new handset as you might damage your device. Rather go to the nearest NSC and ask them to do it. If your handset is older than two years (no warranty) you can do whatever you like. So you can change the front and all other parts so that it looks brand new. If you want to risk it you can do it with your brand new N97 or 5800 with the TORX spanner. More over, you should take a look at the disassembly tutorial before opening the device with the spanner.