You don't have to waste 30 seconds on a full eval when just iterating, I use these one-liners when trying to get some config file working: https://github.com/balsoft/nixos-config/blob/master/flake.nix#L140 ; they only evaluate one specific file and then link it into the right location "imperatively"

Then when I get it working I do the nixos-rebuild switch, which is a no-op in terms of home-manager stuff because the link points to the same location, it just makes it so that it stays the same after a reboot (I use impermanence).