i know their is away to change i think the apple when u start it up to something else, i wish their was a way to change the background instead of plain white. with the new screen it would look nice IMO
As far as I can tell, you cannot modify the existing iPod OS without replacing it (i believe the only alternative is Linux for the iPod... which looks pretty cool).
You can't change the background itself, but you can change some of the built in icons and text by editing the firmware. I successfully used iPodIcons to change the "do not disconnect" icon of my iPod photo to a picture of my dog's face (then it was stolen, so some bastard is out there enjoying my puppy's cuteness 😡 ). Doesn't look like it's been updated for 5th gen, but who knows, maybe it'll still work? I seem to recall this program was smart enough to work with any iPod firmware at the time. Might be worth checking into.