the previous solution was this abomination:

(buildPackages.meson.override { python3 = (buildPackages.__splicedPackages.python3Minimal); }) 

this is basically what I'm trying to do after rebasing to add zlib back in, but what I explained happens

(buildPackages.meson.override { python3 = (buildPackages.__splicedPackages.python3Minimal.override { zlib = buildPackages.zlib; allowedReferenceNames = []; }); })

There's some python3.override's in nixpkgs but they're doing packageOverrides, not overriding python.

python = python3.override {
   self = python;
   packageOverrides = self: super: { sqlalchemy = super.sqlalchemy_1_4; };
 };

There's some python3.override's in nixpkgs but they're doing packageOverrides, not overriding python. (I don't think they cause a python rebuild though)

python = python3.override {
   self = python;
   packageOverrides = self: super: { sqlalchemy = super.sqlalchemy_1_4; };
 };