Remove features deemed 'unnecessary' in upstream Luma3DS
Because these forks are modifications of Luma3DS, they may not always be kept up to date. This is particularly problematic with Luma3DS v10.3 and Luma3DS v11.0, where several changes were made (including copying boot.firm to CTRNAND andchanging config.bin to config.ini).
Installing a Luma3DS fork
These instructions assume you're using boot9strap (as installed in the guide) as opposed to fastboot3DS, where these instructions may not apply depending on your setup.
Because boot9strap just boots the file boot.firm on the root of your SD card (or on CTRNAND), you can just place any Luma3DS fork onto the root of your SD card as boot.firm. Your 3DS will automatically boot into it as it did upstream Luma3DS.
Download your Luma3DS fork of choice
If necessary, extract it and/or rename the file to boot.firm
Put your SD card into your computer
Copy the Luma3DS fork's boot.firm to the root of the SD card, replacing the existing one