You should be able to back the phone up with pc suite and then restore it all when you get it back. Then there is a hash key code for a hard reset to wipe it. As for rebranding - I've never done it but you change the product code back, and then do the nokia software update thing again and it should download and install the correct firmware for it.

I have had loads of problems with the update thing before though, bricked my n96 when I was doing an update once - just stalled and wouldn't do anything then wouldn't turn on. Managed to save it with a different program in the end.