Regarding the unmapping of buttons, I believe I read that this was soemthing that was going to be added in the upcoming patch (2.1) if I recall.

As for switching your crossbars, if you uncheck the "shared cross bar" box in the options menu it will keep each job separate and you can hit R1 to cycle through them. I found this out after playing with the settings. Though, you will have to go back and re-do the bars that were shared for each class.

Hope that helps.