Option to modify existing pybuilds rather than creating a new one
To allow automated addition of new features or updating existing pybuilds via the importer we should add an option to modify an existing pybuild rather than creating a brand new one, keeping existing fields, or re-generating a specified field even if it already existed.
This would make it possible to do things such as checking for mods that need cleaning and automatically fixing such pybuilds, or added sort rules derived from mlox (#1).
Ways to implement code modifications: