Dear aspirant,
Yeah, there is a possibility to change your category but you have submit the original certificate of OBC-NCL caste certificate at the time of document verification.
If you want to know more information about the CSAB special round then you have to check the official website of it. here is the link.
Https://csab.nic.in/cms/Public/Home.aspx
Once you can go through this link and check the business rules. hope it helps you.
Thank you.