There is another thread on this. He wants to use footwear instead of shield, but wants to show it below head and body armor. His original approach involved renaming all of the slots and going through all of the equipment and changing their types so they would show up in the right place. I suggested it would be easier to just change the display order on the equip screen. Someone already suggested Yanfly's script but he had issues with it.
It would be as simple as having an array of slot ids [0, 2, 3, 1, 4] and using the Window_Equip... index to get the slot id from that array, and then use the result to refer back to the actor & equipment, rather than linking directly from the index to the actor/equipment. I believe it would be a very small and simple script, but I just don't have time to write it myself.
Edit: Just saw in the other thread that he got Yanfly's engine working properly, so this is probably no longer required.