You could use a 500 Ohm pot but then you lose resolution. The voltage changes more quickly for less movement of the pot. It would probably be okay with something like a 20 turn trimmer, but it's more likely to get jumpy with wear. All mechanical pots do that, they get jumpy after they get too much wear on the wiper. You wouldn't want to use a single turn 500 Ohm pot, would be too hard to get the voltage where you want it.
You could add a parallel resistor to a 500 Ohm pot to get it down to 200 Ohms, but that's kind of a fail since it makes response highly non linear. It will change too slow at high values and change too fast at low values.
A 100 Ohm pot will not work at all since it will either cut you off for higher voltages or cut you off for lower voltages depending on the resistor you put behind it. Though if you can live with a more narrow voltage range you can use it. Just have to adjust the mean voltage with the resistor value behind it.
I don't understand why they use such a low value resistance to adjust the voltage output. Makes it difficult to use any kind of adjustable value there. I wonder if it's possible to change out the resistor on the board to allow a higher value adjustment resistor. I bet it would be possible, would have to experiment with one.