Hi Joyce

From reading your requirements all I think you need to do is to increase the 'Period window opens before expiration' time from 1 year to something longer.

This would affect every user and the course and activity will be reset when this period starts. People who haven't completed the certification would not be eligible for recertification so wouldn't be reset. 

There is some more detailed explanation of assignment due dates  if the above doesn't meet your requirements.

regards