If you are referring to the Protective Order Governing Discovery, that was requested by Mueller. You might ask why Flynn signed it, but it's no mystery why Mueller did.
-- This whole thing makes me think Mueller is at least Grey Hat? --
I think he is acting true to his form. I doubt he is pursuing any case other than those that hurt Trump. Look at his team. Do you think Weissman, and the rest of the Trump haters, would go after her heinous? Or any DEM minion?
It may be that this action is exactly what Trump wanted. Does that make Mueller a white hat, black hat, or grey one?
-- I'm guessing Flynn will back out of the plea ? --
I'm not sure whose volition that move will be, that is, I'm not sure who will file the Motion to Dismiss. After a bit of thought, I think the "usual order" of having defendant file it would be the better way to exit. Put the ball in Mueller's court to oppose it, or not. So yeah, that would involve Flynn reversing his plea deal.
The alternative is possible, Mueller dropping the charge. Also in that process, I can see some sort of prosecutorial misconduct claims.
-- Do you know who Flynn gave up ? --
I don't think he did, in this venue. It may be that a purpose of this case was to sequester Flynn, so what he knew would not be brought up as "taint" in other cases.
Oops, I see I likely mistook your point here.
If you are referring to the Judge's order to produce exculpatory evidence, that was sua sponte by the judge. If Mueller wants to oppose that order, he has to do so on appeal. He would have to object to it (or it would be best to), of course, in the context of the trial, but seeing as how the order tracks case law, opposing it would be nonsense.
Mueller wasn't given the opportunity to sign it. It was issued to him on the judge's volition.
For many years, the Court has entered a standing order in every criminal case requiring the government to produce any evidence in its possession that is favorable to the defendant and material to either the defendant's guilt or punishment pursuant to Brady v. Maryland, 373 U.S. 83 (1963) and its progeny. The order is entered regardless of the posture of the case when it is assigned to the Court.
From Docket for US v. Flynn, District Court, District of Columbia, 1:17-cr-00232