They changed the speed zone itself or their copy of the ticket? The speed zone can be changed at any time and that would have nothing to do with what it was at the time the ticket was written. But it the ticket was altered, uh, NO, they cant do that.
If you are saying that it was posted 45 at the time you got the ticket and they wrote you for 47 (10 miles over) and then you said - that is not 10 over and then they changed it to 35, they cant do that either.
You need to get an attorney. They can issue subpoenas. Good Luck!
Schertz and Selma are complete speedtraps, everyone knows that!
However, the speed limit is the speed limit, so if you are saying the cop corrected the incorrect listing of the posted speed limit, then yes, he can do that. As long as he is correct about the posted speed at the time of the driving, you are stuck with it. Essentially the citation is a very abbreviated police report and an officer can change a police report at any time.
However, if he has changed the speed he says you were driving I would certainly question whether he is telling the truth now or was telling the truth then.