It gives error messages unless you attach all of the USB disks that are already in the rotation… which is usually not possible… A workaround is to assign a drive letter to the backup disks, and use the drive letter as backup target, instead of “dedicated disks”.
You can normally stop a job with the command “wbadmin stop job”.
However, this sometimes does not work and the command hangs indefinitely. In this case, you can still stop the backup by stopping the “Block Level Backup Engine Service” service. If the service does not stop, use Task Manager to kill the process “wbengine.exe”, which does the same thing.