Copy the existing staff into a new one

I am writing a plugin where I want to turn a melody into chords, based on some rules. I don't want to do this directly on the existing staff, because this would mutate the melody. So, I would like to copy the melody (from the treble staff) and create a base staff, where I will "paste" the whole melody of the treble staff (after modifying the octave, obviously). I am writing my plugin on Windows (Qt version 5.12.x) with MuseScore 3.3 beta 2. What is the easiest way to do this kind of "preprocessing" before I move on to the actual work (iterating and modifying the newly created base staff)?