I would phrase it in relation to the R0! power holder rule more generally. It's not simply negating a game state proposition, it's constituting the ability to declare any game state at a given moment as a valid one, and other participants must accept the R0! game state.
But obviously this remains wholly conditional upon the "consent of the governed".
I wanted to briefly return to this, to follow up an intuition. It was in response to a proposed rule that for convenience I will continue to label "R0!". I am going to make one change to R0! which is that as written it helps itself to an assumption that the wielder is a player, which I want to withhold judgement on. The struck-out text represents that change.
What would rule zero look like, formulated similarly. At first blush, it looks like Under any conditions, this player may declare any other players move invalid; if pressed, they must either introduce a bit of fiction that explains the invalidity, or state a house rule or ruling that explains the invalidity. I contend that such a rule is not a lusory means in Suits's sense. Because in no sense does it establish a "less efficient" means.
Perhaps "under any conditions" works to exclude ordinary refereeing, which has the job of declaring any player's move invalid that does not fall within the lusory-means. They facilitate the sustaining of the proper lusory-attitude by players, whether or not they are a player themselves. Suppose that among the lusory means is a condition that a move is valid iff it either 1) satisfies a game rule, 2) is validated by referee. This isn't speculative - many RPGs contain text to that effect. In this case, the referee is an unnecessary obstacle and counts among the inefficient means that players must adopt lusory-attitudes toward.
That felt like one interesting facet of the proposition. Another emerges on working through what is going on when R0! is followed. The goal of this analysis isn't to quibble over details, but to get into those details just in order to prompt intuitions about what is going on when anything like this rule is followed.
Foremost, the wielder of R0! is going to engage with players, their move declarations, have in mind bits of fiction and prepare house rules. They are going to accept a range of goals and rules of conduct that are unnecessary in the first place. Within that, they will wait upon player move declarations. Why? If the aim is to be efficient, why not rule out such declarations in the first place? This shows that some principles are guiding or constraining them that are not-necessitated... inefficiency-sustaining. As you note, for R0! to function, players must adopt a lusory-attitude toward it.
With "may" the wielder makes a choice - to let stand or invalidate. Their job is not - "invalidate all player moves" - it's - "invalidate some but not others". In satisfaction of "may" they could follow a great number of possible strategies. School themselves to act as a generator of random outcomes. Apply a rubric. Apply some other rubric. Attempt to read the table. Apply one strategy this time and another next time. Apply meta-strategies for deciding which strategy to apply. Follow guidelines written by others. Extrapolate from the rules of the game. Extrapolate from the prelusory-goals. Make the choice least disruptive to the lusory-means / lusory-attitudes. Always validate. Always invalidate. Validate unless the move declaration is put in an unsatisfactory way. Validate unless the move declaration does not legitimate against fictional positioning. And so on.
For the sake of argument, I'll assume that whatever the bar is for "pressed", it is one that sometimes leads to the prescribed next steps. The wielder of R0! must either introduce some explanatory fiction or state a house rule or ruling. Why? That seems highly inefficient to me, but what I find more interesting about this element of R0! is that the wielder's strategy could be to validate in every case except where they have 1) at that moment already in mind a bit of fiction that is explanatory, 2) a preexisting house rule that players are aware of that is explanatory, 3) they make a ruling in a circumstance and manner that supplies explanation.
How that plays out then rests on how each wielder understands "explanatory." It could demand connection with established truths, it could be a proper conformance with no-myth principles, it could entail that they "neutrally and correctly deploy the games action resolution machinery", and so on. Explanatory speaks to the "consent of the governed" - to whom the invalidation is explained. The wielder has accepted a principle that requires decisions be explicable. Of course that could be reduced to "Because I felt like it", yet it can just as well include the sort of principles I outline above and that folk often discuss: maybe the move declaration isn't validated because it doesn't legitimate against fictional position, or it relies on the player helping themselves to something outside their character's mechanical limits, or any number of what I will characterise as virtuous explanations (where virtue is in the eye of the group.)
R0! requires doing unnecessary things in an inefficient way for the sake of players (as part of their lusory-means). Its virtue (or lack thereof) is down to each group, each wielder, their prelusory goals, chosen game text, social contract, and all the other myriad details of their lusory context.