Nimbostratus
CirrusHi,
I always re-initialize the license. You are right. Sometimes it is needed and sometimes it is not. It is a very easy step, so it is someting I always do before an upgrade.
What I should do, is force the Active offline so the Standby takes over. That way you have a early test to see if the Standby works fine. The HA pair might be OK, but maybe something is wrong with the connecting switches or routers. If all is OK, you can upgrade the Active appliance with the knowledge the Standby can take over.
I you do a fail-over during the upgrade and reboot of the Active appliance and something is not right on the Standby, you will have to wait for the Active one to come back online again.
But you plan is something I would do. Upgrade one appliance and test if all is working. If not, do a roll back. If all is OK, upgrade the Standby also.
Don't forget creating Archives and to store them on a external location.
Good luck!!
Martijn