It is a challenging task to write something in addition to Plautus's comedy. Plautus established a fairly strong archetype of humor in the "mistaken identity" element. I think that an interesting and perhaps rather progressive additional scene would involve the auctioning at the end of the drama. The comedy's ending calls for the wife of Menaechmus of Epidamnum to be auctioned off along with the other possessions that Menaechmus owns. Converting everything to cash, the wife is called to be auctioned off. I think that an interesting and humorous twist might be if Erotium has the ability to bid for the wife and both women conspire to teach both brothers a lesson. Perhaps, Erotium could use Peniculus as the agent at the auction, using the payment as the mean that she owed to him.
Once the wife of Menaechmus of Epidamnum aligns with Erotium, they could both devise a way in which they alter their looks to lure both brothers and teach them both a lesson and take the recently auctioned off cash and leave both of them. This sequence is able to work off of the Plautus idea of mistaken identity, provided a way in which both women could transform their looks. Being a courtesan, it seems logical that Erotium would be able to transform the looks of both women to be different in order to ensnare both men. At the same time, this scene inverts the traditional narrative. The ending to Plautus's comedy is where both men are able to come together as a response to mistaken identity. This additional scene would show how women could come together, pulling an idea from Aristophanes' Lysistrata. In making a statement about gender unity, the comic element could be present and add a unique dimension to Plautus's comedy.