tami5: i would think of something like this (in your `configuration.nix`):

``` nix
{ pkgs, ... }:
let
  tpm = fetchTarball {
    url = "https://github.com/tmux-plugins/tpm/archive/v3.0.0.tar.gz";
  };
in
{
  home-manager.users.YOUR_USERNAME = {
    home.file.".tmux.conf".text = ''
      set -g @plugin 'seebi/tmux-colors-solarized'
      run ${pkgs.lib.escapeShellArg "${tpm}/tpm"}
    '';
  };
}
```