my

packages = { ... }         // (lib.listToAttrs (
          lib.mapAttrsToList
            (name: value: {
              name = { lix = "nix"; }.${name} or name;
              inherit value;
            })
            (
              lib.filterAttrs (
                name: value:
                lib.isDerivation value
                && lib.all (n: name != n) [
                  "editline"
                  "boehmgc"
                ]
              ) inputs.nixpkgs.legacyPackages.${system}.lixPackageSets.git
            )

my

packages = { ... } // (lib.listToAttrs (
          lib.mapAttrsToList
            (name: value: {
              name = { lix = "nix"; }.${name} or name;
              inherit value;
            })
            (
              lib.filterAttrs (
                name: value:
                lib.isDerivation value
                && lib.all (n: name != n) [
                  "editline"
                  "boehmgc"
                ]
              ) inputs.nixpkgs.legacyPackages.${system}.lixPackageSets.git
            )

if you use one of the packages in the set, then you want to use the lixPackageSets version. all it does is give the lix version of that package, which is sometimes just overriding the nix version to be lix nstead of cppnix and sometimes a full fork (as in the case of nix-eval-jobs). otherwise, each of those will use cppnix internally

(aiui the exceptions are aws-sdk-cpp, boehmgc, and editline, since those are internal to lix)