You can definitely add a song to Spotify according to your preference, but the process is a bit limited if you're not the artist or the owner of the song. If the song is already available on Spotify, you can simply search for it and add it to your playlists. However, if the song is not available on Spotify, you can request it through the Spotify community forum or contact the artist directly to ask them to upload it to the platform. Alternatively, you can also use Spotify's feature that allows you to upload your own music files to the platform, but this is only available for local files that you own.