You can assign multiple functions to a single button definitely as that's how I used to use it. Can you assign the freeze parameter, that's the question.
From memory turn on stomp A on the Kemper, press and hold stomp A and press a button on the pedal. Press the Kemper pedal button to turn off stomp A. Now turn on stomp b, press and hold stomp B then press the same button on the pedal, they should cycle.