Hello Adnan!

You cannot change your category anytime after the application and  final NEET registration and your admission will stand cancelled if you fail to provide the documents supporting your category during admission. You will be only considered for the category you have chosen initially. And for General Category, you don't need any certificate proofs.

Filling your category as OBC in state counseling would not help because you appeared NEET exam as a general candidate. You do not have OBC rank. You stand at the risk of having your admission cancelled, if you get a seat. The merit list is prepared based on the Category you choose during the time of filling your application form. You must fill your Category as General Category.

Hope you are clear!