To change the keys of a root replica from the replica, use these commands:
replica# nisaddcred des replica# nisupdkeys dirs
dirs are the directory objects you wish to update, (that is, the directory objects that are served by replica).
When running nisupdkeys be sure to update all relevant directory objects at the same time. In other words, do them all with one command. Separate updates may result in an authentication error.
Whenever you change a server's keys, you must also update the key information of all the clients in that domain as explained in Updating NIS+ Client Key Information.