https://github.com/NixOS/nixpkgs/tree/master/pkgs/development/tools/build-managers/apache-maven Above is the apache maven derivation. When I download maven from nix store it creates a settings.xml file in $out/maven/conf directory which I want to overwrite. The requirement is to add a step to the above derivation that will overwrite the settings.xml file. Can this be done by overlays or by overriding this derivation?
The maven package in its current state doesn't follow the normal stdenv phases, but its custom builder does call unpackPhase. This means that you can set variables to influence its behavior.
maven.overrideAttrs (o: { postUnpack = ''
rm $name/conf/settings.xml # just an example; do your thing here
''; })
Technically it's modifying the files before copying to $out, but I don't suppose that will be a problem. If it is, you'd have to split the build.sh script into the usual stdenv phases. Then you could use postInstall.
To use it in an overlay:
final: prev: { # aka self: super:
maven = prev.maven.overrideAttrs (o: /* ... */)
}