So, we just went through the renewal for this and it wasn't as bad in the end.
We purchased 10 new 3-year CA-90 licenses and received the license key.
Claimed this to the dashboard as "license more devices" which meant our CA-90 license limit has now doubled. Then, I went through the process of unassigning the expiring CA license from each camera and applying the new CA license one by one. The license term for the new CA licenses is 3 years from the date the license was assigned to a camera rather than when the license key was generated/claimed to the org.
So, seemed to be OK in the end apart from having the license limit retaining the count from the now expired licenses.
What I am now interested to see is what will happen when our org-wide co-term is up for renewal in 2 years with the CA licenses still extending 1 year beyond the co-term date.