Stickler for "the law" as he just a couple of years ago presented himself to be, now he's trammeled. But watch him wiggle...although he'll try to keep that out of sight, and hide behind a judge if he can...while still pressing forward with the cookie-cutter.
The DA can always pick and choose when to disclose this. The trigger is him wanting to use the evidence. If he doesn't want to use the evidence or testimony of the informant, then he can keep the informant out of sight. On the other hand, if he needs the informant to make the case, his choices are limited to charging, and not charging. This is the day-by-day reality, as prosecutors work to accumulate what they think is "enough" evidence to make the case they want.
-- ... while still pressing forward with the cookie-cutter. --
That has done it's job. Going forward with the criminal prosecutions, Reyna is not stuck with the cookie cutter. He can bring whatever evidence he has before the grand jury, and seek whatever charge floats his boat.
But, in the cases where the accused are suing for deprivation of civil rights, Reyna is stuck with the cookie cutter. He's also stuck with the testimony given by the state in examining trials and similar proceedings.