The default RMAN configuration may be changed as per need. Here is sample configuration change and also changing it back to default setting.
Connect to database using RMAN
$ rman target / nocatalog
# to check the current configuration
show all;
# Configure backups to be written to disk.
CONFIGURE DEFAULT DEVICE TYPE TO DISK;
# Configure RMAN to keep at least 5 backups of each datafile.
# If you have certain backups which must be retained longer than this
# retention policy, you can use the KEEP option with the BACKUP command when
# creating those backups.
configure RETENTION POLICY TO redundancy 2 ;
# Configure RMAN to use two disk channels for backup, restore, recovery, and
# maintenance operations.
CONFIGURE DEVICE TYPE DISK PARALLELISM 2;
# Configure RMAN to write disk backups to the /backup directory.
# The format specifier %t is replaced with a 4-byte timestamp, %s with the
# backup set number, and %p with the backup piece number.
CONFIGURE CHANNEL DEVICE TYPE DISK clear ;
CONFIGURE CHANNEL 1 DEVICE TYPE DISK FORMAT '/oratbkup/oracle/BACKUP/testdb/ora_df%t_s%s_s%p';
CONFIGURE CHANNEL 2 DEVICE TYPE DISK FORMAT '/oratbkup/oracle/BACKUP/testdb/ora_df%t_s%s_s%p';
CONFIGURE CHANNEL 3 DEVICE TYPE DISK clear;
# Configure RMAN to back up the control file after each backup.
CONFIGURE CONTROLFILE AUTOBACKUP ON;
# Configure RMAN to write controlfile autobackups to the /backup directory.
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/oratbkup/oracle/BACKUP/testdb/ora_cf_%F';
# Configure RMAN to use shared Snapshot Control File location.
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/oratbkup/oracle/BACKUP/testdb/snapshot/snap_testdb.cf';
Hope this help. Regards Rupam
