If you are asking is there a way to automate disk cleanup when the disk space threshold is reached, the anwer is no.
What you can do, though, is set the OPP (Overwrite Protection Period) for your media set(s) so that when the data is no longer needed on disk, the BKF files can be reused
You can also use the template provided by Symantec to set up Automatic B2D2T so that when the backup to disk portion of a job completes, it is automatically Duplicated to Tape