It is discouraged to have a dual purpose button on your CP.
That's only true for the KeyWiz.
The single pause/shift button works fine on the Ipac because it's shift function works differently.
Tiger-Heli has a nice page about the shift functions
HERE.
He doesn't address the pause/shift configuration of the Ipac though, which is my preferred configuration of ANY encoder.
If you remap the Ipac so that the Pause button is also the Shift button, and all the admin functions are mapped to P1 buttons, it makes it very difficult to accidentally hit admin functions.