I would need to log every modifications on users access level on projets.
This is why an event on users access level modifications would be great so that a plugin could get it.
Unless I am mistaken, I don't see anything like that exists today.

Minimal information needed are users concerned by the access level modification and on which projects.
Additionnal information could be the old access level, the new one, who did the modifications and the date.

Thank you for your time.