I've changed my category from EWS to UR at the time of counseling if I'll be able to make that EWS certificate can i add category EWS at the time of counseling??

Sarbesh, you have not mentioned which exam or college's counselling you are talking about. I assume it's for NEET since the correction window for it is open now. If not, please specify the exam in the comments section.

Now for NEET, the correction window is open from 15 January to 31 January 2020 and the information filled by this time is considered to be final. You would not be able to make any changes during the counseling period.

So if you can get the EWS certificate before 31 January and can change the category to EWS, it will be valid. Else, you will not be considered for the EWS category even if you submit the certificate during counselling.