Try this powerful tool with a certain MarginNote export format you satisfied（Ominioutliner or Mindmap）:
https://www.pandoc.org
You cloud create OPML through Ominioutliner or Mindmap and then converting into docx by Pandoc.
Also, Pandoc will be an export extension in MarginNote in the future.
Currently OPML export and Python Data Export API is still under development.