if you look at the code there is a set naming convention for buttons and labels associated with buttons. add extra ones of these as required, ensuring the naming convention is complied with. you will then see that the button clicks fire something like
=handlebuttonclick(number)
you will need to set this on new buttons, and then check the code to ensure it handles the appropriate number of buttons.
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the only "catch" with the switchboard is that you should not leave option 1 blank on a menu, or it causes some issues.