Seems doubtful that you would be able to do this at all since licensure postdoc typically involves a contract with the state to be in training as a practicing psychologist, which presumably means you are billing under your supervisor's license. Also, in many states, the board that supervises counselors is not the same board that supervises psychologists. You will likely need to inform both boards of your plan, especially if you plan on using your license at all. Lastly, be aware of scope of practice differences (e.g., can counselors in your state interpret psychological tests?; what are the reporting requirements for psychologists vs. counselors) and avoid billing Medicare, since you can't as a trainee.