If you have not used the tapes, or they have no data on them.
set the tapes to standalone. Delete them from netbackup. Have your barcode rule set correctly. Re-inventory the library, and they will come into netbackup as new tapes.
If the tapes have been written to already.
Wait for all images on the tapes to expire. (time assigned will be blank when they have).
make note of all the tape numbers.
send to standalone.
Delete from netbackup.
Re-inventory library.
They will come in with new Media id's based on your barcode rules.
For all of these tapes you are going to have to re-label the tapes.
Right click tapes, re-label, do NOT check the box to compare the barcode to the written label.
This will then re-write the media id on the BOT to match the barcode.
If you do not re-label and they get new media ids(barcode) then the the next time you try to write to them NB would say that the Barcode and the written media id on the tape don't match and it will not use it.