Following instructions are provided without any warranty, and may even get you in trouble legally. The instructions are provided for testing, learning, preventing e-waste, and should be use with care. We (including contributers + commentators) are not responsible for any damage to your device(s) or any legal issues.
Instructions have been moved to https://github.com/francoism90/asus-router. :)
found the reason, unlike ac88u which can retain these values over reboot, the ac68u forcibly copies the cfe values back to nvram, so you have to add them to init-start.