If you only want to change icons (png files) you can simply open it with winzip or a similar program, change the png files (you must add them without compression), then simply put the modified file in system/apps, I use Root Explorer, but you must change permissions according to other files (rw-r--r--). Copy the modified apk in /system, change permissions and then move it to system/app, then reboot to recovery and zipalign entire system. No need to wipe cache.
Motorola Milestone "CyanoRabbids" - powered by CM7 and my Rabbids theme
Nook Simple Touch "RabbidReader" - Android eBook reader with my Rabbids theme