extension for keyboard mapping: negative harmony?

I recently had some fun playing with keyboard mapping. There's already a "reverse keyboard" option, and I was wondering about adding a "negative harmony"  option, with the option to choose a note around which to mirror. Shouldn't be specially difficult to add from programming point of view, and I would find it very interesting being able to hear my (and other) pieces in negative harmony versions.

(Edit: I just realized I can probably do it already by editing the degree mapping - sorry, I need to learn to think before posting )