iTunes uses a set of unique identifiers on their iTunes store. Each artist, each album (referred to as a playlist) and each track has a unique id. Every purchased audiotrack from the iTunes store contains a set of these ids. It is these ids that are used to connect the code in the iTunes LPs to the tracks in your music library. This however is not done directly. The played tracks and playlists are referenced through XIDs. In the manifest.xml is a list of these XIDs and the track ids to which they are linked.
It would be possible to write these ids to your own .m4a tracks (the tags however are not compatible with id3 for mp3 files), but it requires a specifically modified version of AtomicParsley, which is too much hassle to be worth it. Also it could create conflicts with music purchased on the iTunes store. If for example you use a currently unused pid (playlist id) which later is used for a new album release, if that new release has an iTunes LP it could be referencing your songs, or your LP referencing their songs.
This approach is therefore problematic for any music that is not purchased from the iTunes store. If your intent is to use an LP with purchased music exclusively it might be an option to look into this, however for everyone else there is another option.
iTunes exposes several functions to search the music library for tracks. One is findTracksByXID() which is the default method used in currently published iTunes LPs. Another is findTracksByTextFields() which we will be using in our tutorials and downloadable LPs. This second method allows us to search and play tracks in the music library based on Albumname, Trackname and/or Artist.