how do you play an edited song??

this is pretty simple really. In the game itself, go to the song, and press Up Up, or Down Down to switch to the lighter and heavier modes. Keep doing this till you see that the difficulty mode doesnt change (For example, if you press Up Up on a song on light difficulty, and the game plays the sound of a difficulty change, but the difficulty is still light), then try playing the song you just reached. If that doesnt work, try playing the same song you've been trying to play on the exact same difficulty. If those do not work, then i'm not sure.