It would be nice,
if we can edit playlists that we doesent made but that we just follow and downloaded from Spotify.
Example: Im having a Playlist with Rock songs that I just find on Spotify (that someone else made) for example, and I know a really nice Rock song (which isn´t in the Playlist), that I would like to hear along we the other songs in the Playlist. Than it would be a nice feature, that I can just add the song to the Playlist I just grabbed from Spotify. The songs I add there are only available for me in this Playlist (mean that I just edit the playlist for my own Library, and the songs I add are not synced with the public Playlist).
I hope that your understand what I mean (my english is ok, but was really challenged here xD)
Updated on 2020-03-21
You can create a duplicate of any playlist, which you can edit to your liking. In the Desktop app, click Ctrl - A within the playlist you want to copy to select all the tracks.
Next, right click and Add to playlist should appear. You can add them to an existing playlist, or create a new one.
Hope it helps. 🙂