thesis a refinement of my previous question. I’ve researched this specific customization process. from what is seems, it is only possible to add custom elements to the sidebar.
See the discussion at Example on how to add an element between toolbar of the notebook and first cell of the notebook · Issue #138 · jupyterlab/extension-examples · GitHub
: “Hi everybody,I’m looking for an example on how to add an element between menu bar of the notebook and first cell of the notebook.”
:”…It would be in a side panel, but that is a part of the application that is explicitly designed for inserting your own UX for controlling notebook metadata.”