Over several years/sales I find myself with Celemony Melodyne Studio and Jamo Midi Guitar.
While I don’t see a Aha! moment the two are a match made for one another, some nagging whispers from the back of my brain think there could be a reason to combine powerhouses.
I wonder if you could live sing into Melodyne and make the harmonies specified by MG2?
i can’t see any reason why this wouldn’t work with melodyne studio or any vocal harmonizer / vocal synth software or pedal for that matter.
it might help to have a sustain pedal.
imogen heap uses a keyboard to do this sort of thing and sometimes shifts a single note in a held chord, a nice effect. this might be tough to do on guitar.