There is no correct or incorrect way, if this succeeds.
Ask the person that gave you this advice if this will succeed. I have no idea.
In fact, this method alters system important files and packages, which is the last thing you should do. It’s a very dirty hack and should not be done with a simple copy/paste commands from the web.
The grub method was taken rom oficial ubuntu docs MacBookPro8-2/Raring - Community Help Wiki has worked as the the screen flicker and lines have stopped and also the fans are no longer loud.
When I run the following command, I can no longer see the AMD Radeon card:
Perhaps check the Arch wiki for this laptop and see what documentation is available for a distribution that matches more closely the one you are running?