Ninox, in the case you described just above my guess is that the total load capacitance would probably not be very far outside of the recommended 150-300 pf range for either setting of the Moon's input capacitance. And it's quite possible that you might even be within that range for both settings. So while I would expect the two settings to result in some difference in sonics in the treble region, both settings would have to be tried to determine which is preferable.
A point to be aware of, btw, is that the "0 pf" setting will not really be zero. It will be some small amount of stray capacitance in the connectors and internal wiring, plus some small amount of input capacitance of the circuitry. The "100 pf" setting will presumably be 100 pf greater than that amount.
Regards,
-- Al