Comentário oficial
Hey Andre,
Your music can remain on the external drive - importing it to the rekordbox library doesn't move the music, it just links the location of that file to the database.
If you are editing the ID3 tags on your files directly, you can update rekordbox by selecting any / all of the songs and then updating the tags.
To add new music, I find it's easy enough to add the entire drive as the import, then any songs already imported are skipped.