Moves the wall object to the given coordinates. Doesn't change it's orientation. Wall objects are only visible when viewed straight on, and were never intended to be anywhere but on squares directly facing walls.
Sample use is the gold in the dwarf mines. The gold on the wall is actually a wall object immediately *in front* of the wall in question. This opcode gives the illusion of the gold being mined by moving the wall object to position 128x128, well outside of the map.