Generally, unless you are physically incapable of fulfilling the duties of your role, it is not possible for Disney Internship and Programs Participants to change roles during the course of their programme terms.
If you aren't happy, talk to your leader. It depends on a variety of circumstances and is not at all impossible. During my CP, I was offered a move from merch to attractions as I had a leader interested in my further development in operations, not because I had asked. You never know and it doesn't hurt to talk it over with leaders.