Hi. I'm not sure why you are not able to post in the RetroFab comments since I don't moderate them and anything posted should appear immediately.
Anyway, currently there is no way to assign multiple keys to a button once you've assigned a key :( Sorry.
I'll look into adding the ability to reset the keyboard mappings in a future version.
Thanks for playing and be sure to try posting again in the comments section . I'm always keen to get feedback.