Hey, Karen.
Thanks for getting in touch. The scenario you mentioned is a bit of a tricky one.
If users have completed the certification and on the recertification path, the due date is calculated automatically based on the recertification details and cannot be changed by amending the due date unless you use the certification completion editor or an individual user requests an extension.
Changes made to the recertification period only take effect following the subsequent completion, so changing this would not achieve what you want in this case, unfortunately.
In this case, you could update the due dates for users assigned via a grouping method e.g. an audience, and for those newly assigned users it would push the date forward, however, for those who have already completed the certification, they would need to be manually updated using the certification completion editor. If you have a large number of users, this could be a laborious task to complete! :(
The only way to achieve it would be as you mentioned and that would be to create a new certification with the extended due date. Any existing course completions should trigger certification completions that would put users on the relevant paths with the extended due dates. There is a caveat, though. If the courses added to the certification are used in the original certification, you will likely receive assignment exceptions when you assign the users. You can override the exceptions but I would be wary of this because if the window opens in the original certification for any users, the courses will be reset and it will have a knock-on effect for the newly created certification.
There is more information explaining the different behavioural scenarios surrounding assignment due dates and exceptions in our help documentation, which you might find useful.
As I say, it is a bit tricky due to the logic involved around how certifications work, although, being able to pause and/or extend due dates in existing certifications without any issues would be advantageous.
I would encourage you to flag this to your Totara Solutions Partner so they can provide you with some more support and submit an improvement on your behalf, which our Product team can review for potential future development.
Does that help at all?
Thanks.
Tom