Can you put up a small advertisement on the couplet?

Not so good. This will destroy the integrity and aesthetics of the door couplet. If it is done by an outsider, this behavior is immoral. Couplets are couplets on the door. Source: Lanzhuang in the Ming Dynasty, "Gathering Sound and Letting Xie": "Taste the governor, the door of the book meets the cloud:' There is a spring breeze pen on the shelf, but there is no sunset gold on the door. "