Have you tried my program HARMONY? It does a great deal more, including adding chords, transposing, assigning instruments. (but you have to download it - sorry)

The new version (almost ready!) will have many new features, including abc Lyrics, Songwright export, create a round from any tune, stereo placement of sound within the MIDI file, echo effect, etc.

It also creates Concertina and Melodeon tablature.

It can be found at my web site www.greenhedges.com