Default Softkey Editing is no problem

- Just open the /system/app/systemUI.apk on your PC with WinRAR (don't extract it!)
- Go to directory /res/drawableXDPI
- Drag&Drop ic_sysbar_back or ic_sysbar_res or ic_sysbar_home or ic_sysbar_recent or ic_sysbar_men etc. (landscape, too) to your desktop and edit it like you want them to be
- Drag&Drop them back into /res/drawableXDPI
- Close WinRAR and you've been asked to save it
- Click yes and put the new APK back to /system/app/

Here's the look of my Galaxy Nexus at this moment: