Hi Nilesh,
Currently there is no way to set an expiry date for the certificate. This would be something you would have to develop. Could you not set an expiry on their enrolment so they can not access the course after 2 years? That way they would not be able to get access to the certificate either.
WIth re: to the certificate no. you can use the code element to do this. The code will not change and will remain the same for the issued certificate for that user.
HTH,
Mark