Good job Ardchoille.
Since the tutorial already requires you to use APKManager, why don't you edit it to include decompiling, compiling and maybe a quick note about optimization? They're all options in APK Manager and have more "power" than just changing a couple image files.
With these options, you don't have to worry about .9.png since they'll be compiled with the rest, meaning that you can edit them directly in GIMP or Photoshop. Also, the themer will have access to the "values" folder, where he could edit xml files to change some colors or even text in the ROM (for example the color of the menu and dividers when the menu key is pressed). Or the order of the notification icons. Many things.
Just a suggestion, I know your tutorial is a little more basic though. That's exactly how I started. (I even used Eclipse to compile my .9.png until I discovered APK Manager.)