Simon,

The algorithm is as such: every image on a tape has an expiration date.
After the last image on the tape has expired, the tape becomes available
again.

With BPEXPDATE you can expire all the images on a tape, therewith
expiring the complete tape.

If you use BPEXPDATE to set the expiration date to infinite, or anything
else then expire now, you will do this for all the images on the tape.
To my knowledge you cannot set the expiration for a specific image,
which would not make too much sense anyway.

CU,

Marcel