Hi,
I’ve created a small install script like this:
{ config, pkgs, ... }:
let
apple-set-os-loader-installer = pkgs.stdenv.mkDerivation rec {
name = "apple-set-os-loader-installer-1.0";
src = pkgs.fetchFromGitHub {
owner = "Redecorating";
repo = "apple_set_os-loader";
rev = "r33.9856dc4";
sha256 = "hvwqfoF989PfDRrwU0BMi69nFjPeOmSaD6vR6jIRK2Y=";
};
buildInputs = [ pkgs.gnu-efi ];
buildPhase = ''
substituteInPlace Makefile --replace "/usr" '$(GNU_EFI)'
export GNU_EFI=${pkgs.gnu-efi}
make
'';
installPhase = ''
install -D bootx64_silent.efi $out/bootx64.efi
'';
};
in
{
system.activationScripts.apple-set-os-loader-installer = {
text = ''
if [[ -e /boot/efi/EFI/BOOT/bootx64_original.efi ]]; then
# We interpret this as apple-set-os-loader being already installed
exit 0
elif [[ -e /boot/efi/EFI/BOOT/BOOTX64.EFI ]] then
mv /boot/efi/EFI/BOOT/BOOTX64.EFI /boot/efi/EFI/BOOT/bootx64_original.efi
cp ${apple-set-os-loader-installer}/bootx64.efi /boot/efi/EFI/BOOT/bootx64.efi
else
echo "Error: /boot/efi/EFI/BOOT/BOOTX64.EFI is missing"
fi
'';
};
environment.etc."modprobe.d/apple-gmux.conf".text = ''
# Enable the iGPU by default if present
options apple-gmux force_igd=y
'';
environment.systemPackages = with pkgs; [ apple-set-os-loader-installer ];
}
It builds a bootloader hook that replaces /boot/efi/EFI/BOOT/BOOTX64.EFI. The purpose of it is to enable the iGPU of MacBooks.
For conveniece I’d like to distribute this via the nixos pkgs… But maybe the manipulation of the ESP would go against the guidelines?
If so, do you have another suggestion for how to distribute this to make life easier for MacBookers? 
