[pxc]

Are you referring to impermanence or the erase-your-darlings config?

This tutorial is for Nix itself, not the operating system based on it, which is why it doesn't include install instructions for NixOS.

For a normal NixOS setup with ZFS, traditionally you just partition manually, then mount the datasets how you want for NixOS under /mnt, and the nixos-generate-config command generates a hardware-configuration.nix file which automatically includes all of those mounts for your to-be-installed NixOS system.

You tweak configuration.nix on the target media under /mnt/etc/nixos/configuration.nix, and then run nixos-install and reboot into the new system.