Yes that can happen, but first the prosecutor would have to ask the court dismiss the gross misdemeanor without prejudice and then re-file the case in Superior Court as a felony charge. The term “without prejudice” means the state is allowed to re-file the case if it chooses to do so.
In Washington State, gross misdemeanors are handled by the courts of limited jurisdiction, i.e the District or Municipal courts. Our limited jurisdiction courts have no authority to handle felonies. Thus, if a gross misdemeanor was elevated to a felony, the case must go to Superior Court.
Usually, criminal charges go down in severity and not up. Often charges which are originally filed as a felony get “declined” to the lower court because the evidence does not pan out the way the prosecutor originally thought, or the case upon further investigation simply does not warrant a felony prosecutor. Also, sometimes a “felony decline” may happen as a result of a plea bargain.
Criminal defense is a complicated and serious undertaking. You should contact a qualified attorney to assist and advise you if you are facing any criminal charge.
Generally speaking, since the two are handled in different courts, the prosecutor would have to first dismiss the charges from district court and refile it in Superior court, but yes, the short answer is that if the facts warrant it - a prosecutor CAN amend up.