There was a PR to make overriding go modules easier, and was merged into staging 5 days ago: https://github.com/NixOS/nixpkgs/pull/225051. It may take 1~3 weeks to reach nixos-unstable. You can track its status here: Nixpkgs-tracker.
We may still have some measures to workaround it in the current codebase, though, but I haven’t learned any.
CC @shamrocklee