Do you know that changing the media expiration date has no effect on the images stored on that media?  If your goal is to change the expiration date of an image, whether on disk OR tape, you still need to use the second format "bpexpdate -backupid...".

The first version of the command you listed "bpexpdate -m..." ONLY affects the last date the tape will ever be used for writing further backups, either appending more data to them or if all previously written data expires.  This is because tapes have a basic "shelf life" before they have trouble recording new data, and many installations don't want to trust writing data to a tape that may have been sitting in a slot for a few years.

If all you did was change the media expiration date, your images will still expire from the NBU catalog on their original expiration date, no mattter what the media expiration date is.

bpexpdate -m media_id  will affect ALL backup_ids on said media:

Are you thinking of vmchange?

Change volume expiration date

/usr/openv/volmgr/bin/vmchange [-h EMM_server | volume_database_host] -exp date -m media_id

e.g.

# bpdbm -ctime `bpimagelist -l -backupid client_1316759309|grep IMAGE|awk '{print $16}'`
1317364109 = Fri Sep 30 07:28:29 2011
# bpdbm -ctime `bpimagelist -l -backupid client_1316759498|grep IMAGE|awk '{print $16}'`
1317364298 = Fri Sep 30 07:31:38 2011
#
# bpexpdate -m 300203 -d 12/31/2015 18:00:00
Are you SURE you want to change 300203
to expire on Thu Dec 31 18:00:00 2015 y/n (n)? y
#
# bpdbm -ctime `bpimagelist -l -backupid client_1316759309|grep IMAGE|awk '{print $16}'`
1451584800 = Thu Dec 31 18:00:00 2015
# bpdbm -ctime `bpimagelist -l -backupid client_1316759498|grep IMAGE|awk '{print $16}'`
1451584800 = Thu Dec 31 18:00:00 2015

# vmquery -m 300203 | grep expiration
expiration date:       ---
# vmchange -exp 12/31/2015 18:00:00 -m 300203
# vmquery -m 300203 | grep expiration
expiration date:       Thu Dec 31 18:00:00 2015

Did this give you the info you wanted?

It worked, Thank you Andy!