The basic range of the Randomizer control voltage will be set by the code within the EEPROM, which is further limited by it's 0-5V rails. Unless you want to flash your own EEPROM, you're better off playing with the circuitry after the EEPROM.
The Depth control obviously attenuates the control voltage before it reaches the clock, so you may be able to play around with some resistor values there. You might have better luck messing with the gain structure of the Slew section, it's output, or the resistor voltage divider that biases the Depth control/clock input.