Dear,
Logically speaking after MIGO creating a certificate is not valid.It should flow from P.O only so that user can verify the quality specs at the time of MIGO.
Now i can suggest its better if the stock is not consumed you can reverse those material documents and make a new line item in same P.O and do MIGO.Check the posting dates from MM and FI side while cancelling documents.
Regards,
pardhu