Dear Aspirant 

If you originally belong to general category and by mistake you filled last year obc ncl then definitely you can change your category. But if you belong to Obc category and still you want to appear as general candidate then this is not possible. You can enter in any institute through general category if you don't keep your caste certificate in document verification. 

Good luck for your future :) 

Feel free to ask if you have any further queries.