The statute of limitations on misdemeanors is two years. That means that if a prosecutor believes that she has evidence that a person committed a misdemeanor, she has to file the charge(s) within 2 years of the date of the offense, and after that she cannot file charges based on that incident.
That also means that anytime within that 2 year period, the prosecutor can file charges, and she can change a charge to a higher or lower one, as long as it is done within 2 years. (Plea bargains that include a lower charge could be done after 2 years, if the original charge was already filed.) It is very common for a charge to be reduced to a lower charge as part of a plea bargain. If the lower charge is legally a "lesser included offense" of another charge, it would not have to be filed as a new case, just reduced. If the lower charge is not a "lesser included offense" of the original charge, it would have to be filed withing 2 years.
This answer is intended to be taken as general information and not as specific legal advice. You should always consult a qualified attorney and make him familiar with all the relevant facts in order to get proper legal advice. Every case is different, and they must be evaluated on a case-by-case basis. David N. Smith 812 W. 11th Street, Suite 201 Austin TX 78701 (512) 457-0100 defenseattorneysmith.com