How to get write access to High Sierra (APFS) drive in Read-Only mode on Macbook with faulty AMD GPU
MacOS protects system level files as well as kext files. Maybe the following will help you. Please backup everything up and research it a little further before attempting making any of these changes.

To disable System Integrity Protection:
Boot into recovery mode and enter the following terminal command

csrutil disable


Reboot

Changing Kext Files
To allow yourself the ability to change kext files you should try this:

sudo nvram boot-args="kext-dev-mode=1"


If you replace or edit any kext files, it’s very important you maintain the correct owner and user/group permissions.  You may also need to rebuild your kextcache after changing any of the files within your extensions folder.

To always boot and shutdown in verbose mode
This will help identify hang ups.

sudo nvram boot-args="-v"


To return your system back to normal

sudo nvram boot-args=