Sorry Jitendra! I don't think it is possible as during counselling your marks are automatically filled using your roll number. Even your rank and category score is automatically taken using the roll number of the exam. So according to me you have to continue now as a general Category student. 

Hi there,
Hope you are doing well.
I am sorry to say Jitendra but if you have chosen your category as General during both JEE Mains and Advanced, then you would be only considered for General Category Seats and not for SC Seats even if you submit your SC Certificate at the time of counselling.
Hope it would help.
Thank You