A school board refers to Chang as "a mad man in a Napoleon costume". Chang is actually wearing a Naval Officer's coat. The anchors and Captain's bars can be clearly seen on his epaulettes. Napoleon's uniform had white facings and met in the middle (he often posed with his left hand stuck under the coat.)
When Troy busts through the wall to Chang's office, he inserts his head in the hole he just made, exactly where Chang's face was in the portrait he just destroyed. In the debris hanging from the wall (made of foam to allow actor Donald Glover to break through easily) a hand-drawn circled X can be seen, put there to help Glover hit the exact right spot in the wall to make the "face in the hole" gag work.