Are you saying I can put 40 volts into a stepper motor rated at 12 volts if I use a chopper drive?
Without a datasheet for the motor I can't specify what exact peak voltage your stepper can handle, but in general a chopper drive is designed to limit current when higher voltages are used.
Take note: the motor you have linked is a five-wire, unipolar
stepper motor. Your Pololu driver is for bipolar
stepper motors. The two are not compatible. A bipolar driver will only work with 4, 6, or 8 wire stepper motors.