I bet you don’t know this undocumented feature, even if you have a tape library and is a heavy BAT – Bacula Administration Tool (Linux & Windows Desktop GUI) user.
It is possible to move tape library tapes (load, unload etc etc.) using this graphical interface, especially when changing tapes from/to IO slots is needed, or for tape erasing and disaster recovery purposes.
At the BAT Storage tab, double-click the Tape Library name in order to access the hidden tapes handler, according to the image bellow.
Now you feel free to perform the desired tape changes: