[clever@amd-nixos:~/nixpkgs]$ nix-repl -I nixos-config=/home/clever/nixpkgs/configuration.nix nixos/default.nix
Welcome to Nix version 1.11.2. Type :? for help.

Loading ‘nixos/default.nix’...
Added 6 variables.

nix-repl> config.users.users.isso
{ _module = { ... }; createHome = true; cryptHomeLuks = null; description = "Isso commenting server"; extraGroups = [ ... ]; group = "isso"; hashedPassword = null; home = "/var/lib/isso"; initialHashedPassword = null; initialPassword = null; isNormalUser = false; isSystemUser = false; name = "isso"; openssh = { ... }; password = null; passwordFile = null; shell = "/run/current-system/sw/bin/nologin"; subGidRanges = [ ... ]; subUidRanges = [ ... ]; uid = 231; useDefaultShell = false; }

nix-repl> config.users.users.isso.home
"/var/lib/isso"

nix-repl> :q

[clever@amd-nixos:~/nixpkgs]$ cat configuration.nix
{ ... }:

{
  services.isso.enable = true;
}