Hello Kern
I understand your concerns about make changes by hand in bacula database, but it wouldn't be interesting create an option in update to move volumes to another Storage?
An exemple: you can have 2 disks with 1TB (everyone with one storage) and you will change for a new one of 4TB. In this case is not necessary 2 storages but just one.
You can move all volumes from both 1TB hard disk to the new one 4TB.