Even though some defendants would like to do so, they do not get to pick the prosecutor to handle their case.  The prosecuting office can reassign the case at the discretion of their needs.  This could be for a good reason or no reason at all.  They are not required to give an explanation.  So to answer your question, yes, your case could be assigned to another prosecutor.  If you do not accept the plea bargain before the new prosecutor is assigned, then the new prosecutor could add or change the charges.   If you accept the plea bargain and violate the conditions of your pre-trial probation, the new prosecutor could request changes or modifications of your probation.