To do that your going to have to switch the motor leads from one system to the other, I think it will mean deciding to do this before going on a ride, or carry two 12v batts with associated Leeds or some tricky relay setups to connect the batts in parallel for 12v the series for 24 volt.
Could give rise to mistakes and dead controller and/or pods. IMHO.
Alan
I'd wonder about the practicalities,