If the category indicated by a candidate in the application form for any Examination of the Commission is Unreserved/General category but the candidate subsequently writes to the Commission to change the category to a reserved one i.e. OBC, such request is not entertained by the Commission.but if you filing the form again next year you can change your category as in next year fresh form is accepted in which details needs to be fill again.

If still you've doubt in this matter than don't hesitate to call the helpline of UPSC exam .