Can I changed my attorney for a scheduled court of appeal oral argument?

You can change the attorney, but you would have to pay the new attorney. You can ask the circuit judge to appoint a new appeal attorney but that is not especially likely to work.

Sure, you can retain whomever you want. However, if you are talking about appointed appellate counsel, you would have either ask them to withdraw or motion court for appointment of new counsel & you better have a few really good reasons.