What model of controller?
You should only have to add it as a local controller to the master via
masterip <ipaddr> ipsec <key>
Have the controller sync with the Master, then issue
no masterip
to have it revert back to Master.
If this controller is going to be on the same L2 network as the proper master after you are done doing this, you should turn off ADP so it does not terminate any new APs.
adp discovery disable