vmchange command changes volume information in the Enterprise Media Manager database. Expiration option with vmchange tells EMM that this volume is now expired, which means it can not be used further. Expiration with vmchange will not expire the images and release the media.
bpexpdate - NetBackup maintains internal databases with backup image and media information. These internal databases are called catalogs. Both an image record in the image catalog and a media ID in the media catalog contain an expiration date. The expiration date is the date and time when NetBackup removes the record for a backup or media ID from the corresponding catalog. The bpexpdate command allows the expiration date and time of backups to be changed in the NetBackup image catalog. It is also used to change the expiration of removable media in the NetBackup media catalog. If the date is set to zero, bpexpdate immediately expires backups from the image catalog or media from the media catalog. When a media ID is removed from the NetBackup media catalog, it is also deassigned in the Enterprise Media Manager Database, regardless of the media's prior state (FROZEN, SUSPENDED, and so on). Changing the expiration can be done on a media ID basis or on an individual backup ID basis. Changing the expiration date of a media ID also causes the expiration date of all backups on the media to be changed.