• Target existing books in any namespace by id
• Add categories to existing books
• Add entries to existing (or new) categories
• Overwrite existing content
• Allow adding language content

Adding pages to entries can (for now) only be done by overwriting an entry (maybe by referring to the original datagen of the target mod?), because the loading does not yet handle file merging.

Sample content generated with modonomicon's main project datagen but added as datapack to theurgy: