Dear Beakybird,

To choose the Intro and Ending is quite simple. Just push button E (Left side)in the Main display and again using button E choose the intended Intro or Ending.
During the song playing, to choose other Intro or Ending it's more dificult to continue playing the song without losing time and measures, making that operation.
This is, in this keyboard it seems that the correct way is to choose before playing the song, which I/E we want to use.

Carlos Rodrigues