Can a prosecutor change a charge from one charge to a new charge during a trial?

During a trial, No.  Usually, there are some court procedures that the prosecutor must follow. It is a notice problem.  You need to be aware of the charges that are filed against you, so you can properly prepare for your defense.

However, if during the trial, the prosecutor realizes that he cannot meet the elements of the charge he has filed, he could ask the judge for a finding a a lessor included offense.  Of course, the judge may or may not allow this. 

Hope this helps