Oops, misunderstanding alert!
Nope, nope scrappysim I meant that it's easily doable even with crappy windows paint in 30 sec since the packeges thumbnails is a mere PNG: paste the custom logo you want on your thumbnail, save PNG and import it in your package. No need for any other tool for that. But it would be cool if Postal had an automated process for doing that to put on the CC you want.
Patterns seem to only use the icon png in the package when it is installed via the launcher and a sims3pack.
However bodyshop/CAS thumbnails retain their thumbnail! The hairs packages from Einfach site have a custom CAS thumbnails. Unless it's a different kind of thumbnails, I think there's something to investigate there
Einfach's site is here:
http://einfachsimlisch.ei.funpic.de/Sims3/index.html EDIT: come to think of it, T$R clothes extracted to packages don't have any custom logo... But then how can Einfach do that?