Are you sure about services.udev.rules? I only see services.udev.extraRules in search.nixos.org (which I used already).
I checked other udev rules and nothing else has this tag.
Sorry, I meant extraRules, you didn’t mention you’d used it, but it should work 
If it doesn’t create /etc/udev/rules.d/99-local.rules something is very wrong with your config.
In fact, I did mention it but it wasn’t very obvious without carefully reading 
And yes, it does create the file but it doesn’t have any effect anyway, as mentioned earlier.
For reference: feat(g-aero): add udev rule to always render with dgpu · nicolas-goudry/nix-config@5b901a5 · GitHub