Since each backup job has a pulldown selection under the general section that determines the type of job, Full, Incremental, or Differential, I can see no way you could do this. If it were me, I would set up three jobs. First, a full backup job for Friday that backs up everything, called something like Friday Full. Next, a full backup job that backs up the folders that must always be done with full backup, called something like Daily Full. Third, a differential job that backs up everything else that just needs a differential backup, called something like Daily Differential.
Then you schedule the Friday Full to run on Fridays only and to overwrite the media. Schedule the Daily Full to run on Monday through Thursday at say 8:00 PM, or whatever time you normally schedule for. Set it to overwrite the media. And finally, schedule the Daily Differential to run Monday through Thursday at say 8:30 PM and set it to append to the media.
This should give you a tape, or set of tapes every Friday that contains a full backup. Monday through Thursday you should get a tape or set of tapes that contain a full backup of the folders that need full backup, and an appended differential backup of all the other files that have changed. It really doesn't matter what time you set the Daily Differential job for as long as it is after the Daily Full. It will start the Daily Differential job as soon as the Daily Full finishes. The Daily Differential job will attempt to start but will go into a queue status waiting for an available device to come ready.
I can't think of another way to do it, but if anyone knows a better way, I'm all ears.
