Yeah, been playing around with that method for a while using GIMP to set some themes/device images.
Certainly not the greatest resolutions, but fun to see what it can do. For instance, took all of the left and right and "center" buttons from the 980 file and shrunk them to work with the 780 (the stock ones leave a bit to be desired), then added a few of my own (Wii U, Off), and some master pages (e.g., when you hit the "Wii U" macro it just takes you to the page below).
Kind of fun. Have 2 themes setup thus far (really just two sets of buttons as you can see below and different backgrounds). The buttons on the dimmer pic below for instance give the impression that the buttons are actually being pressed when you hit the hard button.