If you maintain the Excel workbook with the required structure and save the document as a mailmerge main document, the setup is a once-off exercise.

You can add bookmarks to your mailmerge main document to aid its navigation, but any bookmarks will be deleted from the output document. That's because a mailmerge typically generates multiple replicas of the mailmerge main document in a single output document, but a bookmark can only exist in a single location.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]