it is undocumented, but obviously settings are saved in:
~/pronsolerc
there are lines, one for each buttons with this syntax:
button 0 "label0" command0
button 1 "label1" command1
...
If you right click on a button you will get a menu with "edit" "move left" "move right" and "remove"
Clicking on move will change order by one step so you may have to click severel times if you have major changes.
