Oracle Error Message
RMAN-05021: this configuration cannot be changed for a BACKUP or STANDBY control file
Reason for the Error
The user attempted to modify the configuration which cannot be changed for a BACKUP or STANDBY control file while the mounted control file was either BACKUP or STANDBY. The following configurations can be changed only when connected to primary database instance that has CURRENT/CREATED control file type mounted: CONFIGURE RETENTION POLICY CONFIGURE EXCLUDE CONFIGURE ENCRYPTION CONFIGURE DB_UNIQUE_NAME
Solution
Connect to primary database instance and execute the command.