I have re-organized the MY TAG editor. Created tags with "playlist names". So I can mark a checkbox on each track in which playlist it has to appear (one or more...). The next thing you have to do is replace all normal playlists with intelligent playlists, filtering on that particular tags. Then, when you change the tags of a track, it's automatically moved/deleted/added, to/from one or more playlist.
This works awesome! Personally i think this is one of my best experiences with rekordbox :-)