Dear Swamy 

The students cannot change their category after the acceptance of application form and obviously after NEET results too.

However, If any candidate belongs to category(ST/SC/OBC/PwD) and not able to produce the caste certificate at the time of counselling, the authority itself is well authorised to consider you as general category and position/ranking of yours will be listed in general category list.

So, you don’t have to worry about that, you can avoid giving the caste certificate and you will automatically recognized as general.

Hope this helps you.

Good Luck.