After signing a Air Force contract with the job & ship date stated Is it possible to Change your job in DEP?

I am a Pararescue DEP I signed my contract with the air force which specifies my job and the date I will be shipping (Feb 2nd). I am not sure that this is the job for me and would really like to be a SERE instructor. Is there anything and I mean anything I can do or ask for to make that happen.