This is how I do it
https://github.com/RossSmyth/nixos/blob/main/mkMachine.nix

Works well enough. I also have a bash wrapper about nixos-rebuild that does things like:

1. nom
2. -I $(npins get-path nixpkgs)
3. --attr $(hostname)
4. --show-trace

sorry i was on my phone and should have looked it up before saying that.
i actually meant .overrideScope, which will allow you to have the correct lix derivation used by other derivations in the lixPackageSets.latest set.
for example, you'd do something like:

finalPkgs: prevPkgs: {
  lixPackageSets = prevPkgs.lixPackageSets.extend (finalSet: prevSet: {
    latest = prevSet.latest.overrideScope (finalScope: prevScope: {
      lix = prevScope.lix.override (prevArgs: {
        curl = prevArgs.curl.overrideAttrs { patches = []; };
      });
    });
  });
}