If you want to duplicate a NetBackup image from the command line, you can use the bpduplicate command.
bpduplicate -backupid
So for example, you can run:
bpduplicate -backupid testclient1_123456-dstunit Linux_Staging -set_primary 1
The command above will duplicate the testclient1_123456 image onto the Linux_Staging storage unit and it will set the copy as the primary copy.