There is no surity of this process, but while IIM-Rohtak was conducting CAP last year they had cases in which people had old NC-OBC certificates at the time of interviews. So such people if selected were required to produce current FY Nc-OBC certificates after giving a LOU to the institute and drafting an official mail to the Admission committee. Your case is quite different although you may still follow this process and Draft an official mail to the Cat conducting IIM. In case if they had previously given a specific time period to edit your Cat Form Response than there are 99.99% chances that they wont reconsider, but you should still try, for a little hope still remains.

I hope this helps you.

All The Best!!

SMIT-IIM-AMRITSAR-PGP/04