to change a wallpaper you can just drop the image on your sd card and select it, or you can drap drop it into the drawable hdpi folder with the same name as the wallpaper found in there already. there is another, i believe you can replace as well in one of the other drawable folders.
to change things around entirely you can open to counts of 7zip; one with the things you want to move in to the other, the other that you want to change things in.
then going from same folder to same folder; drag drop the image you want moved in to the other 7zip. then close 7zip and boot theme.
ex.: i want a status bar from theme A and to keep the rest of theme B.
open theme A in 7zip and go to drawable hdpi, find status bar png (image file for status bar), open theme B in another 7zip to same folder as theme A.
drag drop the status bar png from theme A in to the same folder of theme B. it overwrites the old status bar. close 7zip and boot theme. i now have the new status bar in my other theme.