You can try this:
- Backup the flash on all controllers and copy them off the controllers.
- Add a VRRP to the existing master's management VLAN and make the master a priority of 200 on that VRRP.
- Change the masterip on your local controllers to point to the ip address of that VRRP (will require reboots of those controllers).
- Validate that they show up on the existing master, as well as all of the APs.
- Add the new master as a backup master
a- prepare it to make sure it has the same version of ArubaOS as that master
b- create a VRRP with the same number with a lower priority on that same management vlan.
c- make sure it becomes a backup to the master on that VRRP.
d- configure master redundancy and reference that VRRP.
e- Type "show switches" on the current master to make sure that it sees the new controller as a backup master
- If you remove the original master, the backup master should take over and have a copy of the centralized licensing database, as well as the cpsec whitelist.
You will have to test all of the steps above, because you might have things configured in a way that will not allow the general steps above to work. If you feel uncomfortable about the steps above, please contact TAC for them to walk you through it.