Carefully unplug the pickup leads (do not pull on the wires, grasp the brown modular housing) and switch them (plug the one in where the other one was); that should reverse the pan control.
Looking at the pictures for a while, it seems to me that perhaps it might be possible to switch the pan control and the filter. If so, you would remove the knobs (each of the knobs has two very small hex head screws, both need to be loosened, be careful not to drop them and lose them), then the nuts that hold the controls to the body. Pull the PC board and the smaller control out and move the ferite bead out of the way for the moment. Position the PC board so that the control is in the other hole and the far end is angled up toward the top of the battery. The other control will go back in the top hole, and the ferite bead will go wherever there's some remaining room. Make sure the PC board doesn't touch the volume control or the shielding.
That's my guess anyway, you should be able to tell better than I if it would work. A ruler might help. You'll want to make sure all the wires will still reach where they need to go. Others may have more useful opinions on whether this would work.
