note, you can disable SIP, make your changes, then re-enable SIP. It doesn't have to be left off all the time. The changes made by LiteIcon appear to 'stick' and El Capitan does not complain. A bit tedious if you want to change icons constantly, but for those us like myself, who change it once in awhile, it's fine. Also, note that in the shipping version of El Capitan, using this command:
sudo nvram boot-args="rootless=0"
no longer works. you can set it, but it is ignored. The new method is using the CSRUTIL from Terminal WHILE BOOTED INTO THE RECOVERY PARTITION.
> csrutil enable
> csrutil disable (turn off SIP)