No, there aren't any controls to adjust the cutoff frequencies. The "crossover" at the HU end has a simple high-pass filter (just a resistor and capacitor) on each of the positive lines going to the 4 speakers. Someone mentioned the values in the thread on IWSTI (so it should be possible to calculate the cutoff frequency).
The harness sends full range to the sub. The sub obviously has its own low-pass (and no means to change whatever frequency that is).