You can do the same thing that customize do, but manually. You have to explore a little bit into your springboard app and you will be able to change it. This is the way to do it.
You have first to ssh into your phone and locate every single icon you want to change. You can find a very useful list here to start:
http://www.hackthatphone.com/111/iphone_graphics_locations.html
Once located, you can customize them. As you probably know the iPhone icons are compressed with a strange png format. You won't be able to read them on your computer. You can donwload the fixed png from the same site that has the list. You can use photoshop to customize your icons, put the same name they have on the springboard and replace them.
Otherwise, you can download the customize themes and pick the already changed icons you can find on them. Just go to installer and install them, you will find them on var/root/library/customize or on var/mobile/library/customize depending on how old is the theme.
ALWAYS, always! keep a backup of your icons in case you mess around with them and you finish with no icon on your springboard, then you just replace with your fresh backup and everything comes back to normal.
Changing the springs is more complicated and the only way I found is to pick an already changed spring from a phone with 1.1.2 with a customize that works. Changing it manually is too complicated for me
Good luck and have fun.
By the way... thespicychicken said that he would release a new version for customize in about 2 weeks, so... if you're though enough to wait...
