if you had a chord selected in a midi editor, could an extension or plugin invert it? I guess it could read the notes, and then change them in some predictable way?

Did you try the "Scale" function in conjunction with "Chords" from the context menu already? Selecting notes that build a chord and shifting them up and/or down is quite a fast way to invert individual chords where needed. -Data

That - in other aspects - is normally the way I do things. :eek: -Data

There's are invert horizontaly and verticaly actions in action list (in "edit") :)