Changing WPILib's code is a bit risky, I wouldn't do that. You could, however, write some classes of your own that demonstrate similar principles. What I would do is define a "ToggledPressedButtonScheduler" class:
http://pastebin.com/agFtqpAN
http://pastebin.com/bZwmbD21
It's based on "PressedButtonScheduler", but starts a different command every time the button is clicked. Here's how you should use it:
http://pastebin.com/SmBGNhFu
Please note that the code was written in pastebin and was not tested (or compiled).