Update: Shattered Husky has been replaced by Theme Lab: Converter. It's also free and better in just about every way. I am leaving this up just because I don't like the idea of removing stuff from the internet but there really is no reason I can think of to use it.
Shattered Husky allows you to convert any winterboard theme to the IconBundles format. This means you can use a theme built for iPhones on iPad, and across any iOS version.
To convert a bunch of themes at once, open terminal or command prompt, and navigate to the directory of Shattered Husky.jar Then type: java -classpath Husky.jar BatchConverter
To use Shattered Husky
- Copy theme to your computer from /Library/Themes on your device using iFunBox, iExplorer, (in combination with the Cydia tweak "Apple File Conduit '2'") or OpenSSH.
- Convert the theme by running Husky.jar. Put the converted theme back on your device in /Library/Themes.
- Apply it in Winterboard settings.
Here's a tutorial.