Hello student,

Hope you are in best of your health, so the answer to your question is yes, after the JEE registration you can give the EWS certificate . As after giving the exam JEE main have made available the correction window where you have to give the scanned copy of  EWS certificate , there you have to provide the EWS certificate . Also I would like to tell you that you should made available your EWS certificate before the time of counselling if you are thinking to go through General EWS category.

Hope this helps!