(absolutely not your fault 
, but there was a fairly similar request not very long ago, and what started out as a genuine offer to find some kind of solution degenerated to the point of no longer wanting to “help” further ).
So, starting afresh …
Question #1: The notes that are already in the MIDI Part, are they therefore unimportant to the end result?
If so, I think I can see a two-stage solution (albeit a bit complicated to actually set up)…
Step #1: Like you have already pointed out, use the Transformer Insert FX to randomize those notes (giving you a set of completely random notes on output… up to yourself to decide the necessary range).
Step #2: Add the Chorder Insert FX into a 2nd slot, and for each of the possible incoming notes (i.e; fed from the Transformer), assign an outgoing note that is for example, either C, E or G (maybe in different octaves, for greater variety).
So the result should be as follows…
For each note that is already in the MIDI Part, a totally random note will be output to the Chorder, and the Chorder will output the note that you have assigned to that received note.