Is it possible for a voltage multiplier to be used to provide both positive and negative voltage?
if you connect a capacitor to the top right node, and an ac source to
that capacitor, can it produce dc voltage with the reverse polarity? I
think it looks like it would because the diodes would be in the
opposite polarity relative to the capacitor.

If you mean this: -

Then yes but you'll still need another set of diodes and capacitors to keep your positive voltage. If this is not what you meant then I suggest you draw a picture of what you mean.