The same song can have different playback settings where it exists in more than one library (Main library and other playlists it might be in).
This is useful when you play/sing the same song in different ways—sometimes as a Bossa or a ballad, or want a practice version in a different key, or where you play the song in different bands or with different singers who sing it in different keys. Each can exist in a different playlist with different settings.

These settings are:
- key
- playback style
- tempo
- repeats
(Mixer settings volumes, instrument choices etc. are NOT stored with the song.)

Open the song from the song library or playlist where you want the settings for that song to be changed. Change the necessary Song settings. They are now retained for the song in that playlist library.

Duplicating a song* in a playlist (or in the Song library) will add the duplicate song to that playlist (as well as the main Song library) where it will initially inherit the song settings of the song in that Playlist (they can then be changed if desired). For example, you might want to use a different style and/or tempo to the same song so either version can be selected in a single playlist.

Exporting (Share) the song obeys these settings as you see them for the song chart. Check these settings before sharing to make sure you are sharing the correct version and its settings (from its playlist) of the song.
(The song's settings also apply to exporting the audio file or midi files of the song.)
 
* you will have to add some text or change a chord(s) so the song can be saved. If you make no changes to a song you have just duplicated, it will not save until you alter it in some way. Some like to change the title slightly to differentiate it from the original or label it with its purpose or band/singer name etc.
 
Additional
If you change a song's style in Song info (the style name showing in Song view, top left) and a similar/matching style is found from the player styles (built in styles or IAPs), then any saved song style for that Song's settings is deleted on saving, with that style now showing as the playback style in song view.