You can add your own packages to systemd.
{ config, lib, pkgs, ... }: {
systemd.packages = [
(pkgs.runCommandNoCC "toplevel-overrides.conf" {
preferLocalBuild = true;
allowSubstitutes = false;
} ''
mkdir -p $out/etc/systemd/system/service.d/
echo "# Dummy" > $out/etc/systemd/system/service.d/toplevel-overrides.conf
'')
];
}
If you want to use this with template units you have to change it a bit, see Declaring instances of a generic systemd service e.g. `my-service@foo`? - #5 by hmenke