This guide has been written originally by Ivan Alex HC
Before making extreme changes, take the following precautions:
adb shell):dd if=/dev/block/bootdevice/by-name/system of=/sdcard/system.img bs=2048
adb push RestoreSystem_signed.zip /sdcard/
RestoreSystem_signed.zip file from Recovery. Once the process is complete, a system script will reinstall the stock version of the recovery on first boot.Repeat this procedure every time you decide to start customizing only the system partition.