[Kevin]

If it violates the Student Code of Conduct, I'd say so.

In this case, your hypo did not have the Cosplay Club having been previously removed from school and students forbidden to join. So you can join this Club.

If, however, the school finds that the Freemasons violate school rules regarding diversity and inclusion and thereby ban students from associating with the FreeMasons, I would think students who associated with the Freemasons could be subject to discipline.