I have compiled, and subsequently archived, a large variety of m3u playlists over the years. Many times, my music file library got shuffled or moved around to accommodate an ever growing music collection. Every time this happened, the playlist-mapping to the music files in the database was lost, to be retrieved only with huge effort - if at all. Then I discovered this ingenious little app called ListFIX() that effortlessly restores the playlist-mapping to the current database.
Maybe you will find it as useful as I did. You may find it here: ListFIX()