Surely he can't do that; you can't put the toothpaste back in the tube.
Happens all the time. I was in a certain missile program that was, as they say, "mature". By that time video and photos of the warhead detonation pattern had appeared on TV and in print many times. Very late in the game it was decided that stuff should be secret, so we removed a couple of the photos on the banner hanging in the factory. Not a dang thing we could do about the information in the public domain.
But "officially" it was now classified, and anyone who had a clearance could be penalized if they let the images be comprimised.