Yes,
merch should be allowed. It can be used as a casual term for any kind of merchandise, but is most often used for products associated with a band, sports team, political campaign, etc. In these senses, Merriam-Webster dates it to 1982, while the online Oxford gives it an origin in the 1960s. Either way, it wasn't much used until this century, and has become quite widespread just in the last few years - see this chart from the News on the Web Corpus:
Despite the growing usage of the word, I suspect it hasn't made itself known to all our players, so I'll make it a rare word for now.