What is the name of your state? TX
I was offered a reduced fine and deferred disposition by the prosecutor. I opted to proceed with a jury trail. Suppose I change my mind the day of the jury trail, would that offer still be good?
It's possible, but I certainly wouldn't count on it. When the prosecutor offers you a deal to avoid trial, it is usually a better deal if he hasn't had to do a bunch of work on the case. If all he has done is read the police reports and reviewed the case file, he hasn't wasted much time on the case and so he makes you the best deal he figures your situation deserves.
But when you don't take the deal, you force him into having to prepare to take the case to trial. This is allot of work. Work he was hoping to avoid when he offered you the deal you didn't take. So after he has gone through all the research, witness interviews, investigations, serving subpoenas, filing motions and changing schedules so he is available for trial etc etc., there isn't much motivation left for him to settle the case. The work is already done, he's only got to present it to a jury at this point and he figures you made your choice and didn't want to work with him when it was to his benefit to do so as well as yours. Now, at this point, it may only be to your benefit to take the deal and so it probably will not be offered again. The only chance of it still being on the table at the time the trial date arrives, is if he/she thinks the case against you is weak and therefore not confident in getting a conviction.
But if the evidence against you is strong and there are plenty of witnesses to the crime you're charged with, plan on it going to trial, as the big deal of the day will no longer be an option available to you.
The deal will be on it's own
trail, the long gone trail...