Hello Aspirant,

No you cannot change your category neither in JOSAA counselling nor during JEE=Advance application process, whatever the category you will be filling in JEE-Main application would be considered as your final category. Now see you can get a middle way if you don't have your EWS certificate right now, that middle way is self undertaking. If you belongs to EWS category and you are sure that by the time of admission process i.e. around the month of May you would get your certificate then you can submit self undertaking form which will be available there in the information brochure released by NTA for JEE-Main 2022, which declares that you will submit the original and valid caste certificate later on at the time of admission. So you can fill it for EWS reservation and then at the time of counselling and for JEE-Advance you can get the benefit of EWS reservation.

I hope this information helps you.

Good Luck!!