I have purchased the enhanced version of the Testors Custom Decal System software, so I can custom make decals and import designs into decal form. I don't know if anyone here has really played with the idea of putting water-slide decals on figures, but I am planning to do just that with some clones. Specifically, just as Neyo's legion only had that little red circular symbol, I'm thinking of doing another legion that is distinguished by a small symbol. I figured decals were the way to go. I also figured decals may be the way to go for the shocktroopers--at least for the forehead.
I'll share as I go throught the process. If anyone else has tried it and wants to share their experiences, please go ahead.
Edit: Now I'm fully aware you can use any program to design stickers and can print them out to decal paper purchased anywhere (again, please share experiences), but I personally can make a couple of quick recommendations about the Testors Product. Do not buy the (approximately) $7.99 set at discount stores. This set will not allow you to make custom graphics, nor will it allow you to import new graphics. It also only comes with a couple of clear sheets and a couple of white sheets of decal paper. Instead, if you want to go with Testors, go to http://www.decalgear.com/DG/ and click on the standard edition. This program will allow you to create and import. One warning though, buy the decal paper in either clear or white, because the standard edition on the site doesn't come with any.