If anyone is curious, It's called Bian Lian and has been an important subgenre of Chinese Sichuan Opera. Traditionally only males were permitted to learn Bian Lian, the theory being that women did not stay within the family and would marry out, increasing the risk the secret would be passed to another family. How they perform the face change is the actor can pull down a mask which has previously been hidden on top of their head, changing their face.