Methods for updating an already existing SBOM

[SamuraiAku]

A likely use case is that someone uses PkgToSBOM to create an initial file, then makes their own additions and modifications. It would be very helpful to be able to read that file and be able to update the parts that need updating while leaving the user's other changes untouched. Examples are licenses, comments, files, snippets, etc.

All this package is made to work with are packages and relationships.