If a customer physically attacked me at work and was only charged with a misdemeanor, when we go to court can I have the charges changed to assault?

First, you would be considered the victim in this case, not the offender. The offender is the person who assaulted you. It will be up to the prosecutor to determine what the charges will be. The prosecutor has to determine if the facts/circumstances in your case meets the legal elements necessary to charge the offender with an assault. If you believe this case has been undercharged or charged incorrectly, speak with the local prosecuting official handling this case and ask that they review the charges in hopes they will amend the disorderly to an assault.