I successfully changed my background (to one of the stock silver metal looking pre-loaded ones), but the rest of the screen (AV screen) graphics (touch screen buttons, album name, etc) are still the stock Pioneer blue motif, which doesn't go well with the different background, so I changed it back. Is there a way to change those button etc graphics too?

Not that I am aware of, I think we can only change the background pics only...

No, those images can not be altered. Only on the F series unit can you do that.