T520 question

Hi,
I am planning to install HighSierra in a T520. I am planning to use tluck's T420 guide. tluck's guide uses integrated intel graphics and a display resolution different than mine.
My laptop screen had 1920x1080 resolution, and I use an external monitor with 1920x1080 resolution. Since I want the external monitor to work, I also want the nvidia nvs 4200m card to work. Since Optimus won't work in OSX, I am planning to switch graphics in BIOS to discrete.
Can anyone suggest the changes I need to do from tluck's method.

Thanks.