Quiz

I don't think this is possible to do retrospectively. However, you could make it work in the future by using the Group override facility. Create a special group called "Medical Cert", and then add a Group override for this group in each quiz. The override settings should disable the open and close dates, but have a unique secret password, and only 1 attempt allowed (see screenshot below). Keep the list of override passwords for each quiz somewhere safe, and when a student needs to complete a quiz they missed, you just add them to the group, and send them the password for the quiz they missed.

What you are seeking, Francesc, has been asked for in the past. As far as I know, this feature does not exist. Eoin provides some ideas using "groups" to make overrides for a group of students. But in your case, your focus appears to be making a bunch of changes for only one student.

So, the problem with "exceptions" is that they always take more time to manage. That good old 80/20 rule kicks in, 80% of your time could be managing exceptions, for example.

Your idea has merit, but as I think about it, the "logic" to do this could get quite complex. For example, you would probably want to use some kind of "offset," such as "give this student two extra weeks for all assignments." But "All?" Or "some?" And always two weeks, or sometimes three, four, etc? And some folks might say "for this student, every assignment is due on May 14th."

I am just trying to point out some of the complexity of doing "mass" changes.

You might want to search the Moodle Tracker system to see if someone has made this suggestion. If not, you can start one on your own. But make sure to provide as much logic as possible about how you see this feature being implemented, including the User Interface.