Can you change your plea from guilty to not guilty?

yes.

You don't plead guilty "on a traffic ticket" unless you post your fine and then fail to show up at the hearing. That is an automatic guilty plea. If you to go to court you may plead not guilty to the...

Yes, you can.

Up to a certain point, yes. It is not helpful to your defense, though, but if you can successfully defend yourself then it is worth the time.

How soon after you orignally pled before you decided to change you rmind? You can file a motion/petition for a change of plea, or a re-hearing, giving your reason(s) for wanting to do so. The judge...