A: Technically, the only in-game effect of “Stop That Singing!” is to remove the Rule “I Just Want To Sing”. The statement “…and forbid all players from singing,” means that when you play this card, you essentially just read the title forcefully: “Stop That! No Singing!”

As an Action, it’s a one time card, so it goes away, and the results of your declaration are expected to be about as effective as in the movie…