OK, thanks Sergio. This makes sense. Did you disable SIP before the hack? Or is there anything else that should be done, other than you listed, before or after the hack?fsck -fy checks the integrity of the files system. I did in just in case especially if the system had been shutting down abruptly because of the graphics problem fsck -fy will correct any errors on the OS.
Yes you can use a normal user with admin privileges to remove kext from an external OS installation. In my case I did it the other way, booted the system with an external drive <opt> on boot and then choose to boot from the external drive, already without the kext, and then use the external system to find and remove the kext from the internal drive. Hope that makes sense to you.
I would use the same method for upgrading in the future, if you have access to an external drive with an installation of OS. Boot from the external OS and then use it to upgrade the internal disk and then use it again to remove the kext. This way you don't have reapply the hack.