I have a fairly special setup, using Linux on a MacBook Laptop.

to switch off my secondary graphics card in it I'm required to add these lines to my grub

outb 0x728 1

outb 0x710 2

outb 0x740 2

outb 0x750 0

I do this by pressing 'e' for my selected grub menu option and adding the lines one by one . then finally booting . But as we know it's not permanent.

I cant really figure out where i need to add it for grub to always append it to my Linux boot options.

It's doesn't seem to belong in /etc/default/grub
since here i can add stuff to the kernel boot line

Honestly i'm afraid to fiddle to much with grub on my computer since getting it to triple boot Linux/Mac/Windows was a very delicate and timely matter.

Does anyone have any idea of where to add it?