This glitch requires that you own a new home plot in the "Hearthfire" DLC. Construct an armory in one of the wings. Once the armory has been constructed, you will be able to display armor on the mannequins inside. Place the desired armor set to be duplicated on the mannequin, then leave the room. Next, take the armor off the display, then leave the room again. Go back to the room, and the armor will have been duplicated on the mannequin. Note: Whichever armor set you first put on a mannequin will remain there; you will not be able to switch it out. Thus, if you want to duplicate a different armor set, you will need to use a different mannequin.