# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, lib, pkgs, modulesPath, ... }:
let
  dashFile = "some_file.txt";
in
{
  deployment = {
    targetHost = "x.x.x.x";
  };
  networking.hostName = "HOST";
  home-manager.users.su = { pkgs, ... }: {
    home.file."dash.sh".source = dashFile; # dashFile is a variable declared above
  };
  imports =
    [
      ../lib/dashboard.nix
      ../lib/wifi.nix
    ];
...
}

So that's the node.nix file

# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, lib, pkgs, modulesPath, ... }:
let
  dashFile = ./some_file.txt;
in
{
  deployment = {
    targetHost = "x.x.x.x";
  };
  networking.hostName = "HOST";
  home-manager.users.su = { pkgs, ... }: {
    home.file."dash.sh".source = dashFile; # dashFile is a variable declared above
  };
  imports =
    [
      ../lib/dashboard.nix
      ../lib/wifi.nix
    ];
...
}

So that's the node.nix file

And from flake.lock

    "colmena": {
      "inputs": {
        "flake-compat": "flake-compat",
        "nixpkgs": "nixpkgs",
        "utils": "utils"
      },
      "locked": {
        "lastModified": 1630033162,
        "narHash": "sha256-1Vh0d2t2aSfvEXx1iQ1TRNpFfncTE3G+T0Co+dRppBo=",
        "owner": "zhaofengli",
        "repo": "colmena",
        "rev": "37b43cd6d7f924e6eb7eaa7b17852d813cf96c31",
        "type": "github"
      },
      "original": {
        "owner": "zhaofengli",
        "repo": "colmena",
        "type": "github"
      }