Follow the below steps to rename a host in BackupPC.
1. Stop BackupPC service :
service backuppc stop
2. Login to the configuration folder
2. Change the host file to the corresponding one :
*change old_host to new_host*
3. Rename the pl file in pc folder :
mv old_host.pl new_host.pl
4. Make the changes in the backup location (I assume your backup is storing in the location /backup):
mv old_host new_host
5.Start Backuppc service:
service backuppc start
6. Login to the backuppc console and make sure that the changes are replicated there.