Bnei Yissaschar, Adar 9:1/בני יששכר·אדר ט׳:א׳

1In this it will be spoken about the commandment of the Purim meal, and that a person is supposed to become 'spiced,' etc. And the name of this essay is, The Party and the Joyful Occasion:The custom of the Jewish people is [considered like something from the] Torah. They have followed the practice to change into different clothes during the meal and Purim party, and 'this is not an empty matter.' So behold I have contemplated 'from the lattice' at the Torah (creative work) of the famous rabbi, our master, the rabbi, Moshe Chagiz - that it is in memory of that which our Rabbis, may their memory be blessed, said, "They only did it (when they bowed down to an image in the days of Nevuchadnezzar) on the surface (lefanim, which is related to the word for face); so too did the Holy One, blessed be He only do it (the decree of annihilation) on the surface with them. Hence they change their clothes at the time of the joyous occasion, so that it will not be known whose face it is. This is something pleasant concerning the simple understanding of the custom.