I got into a situation where I missed tape changes for a few days, so
  my backups we put to the holding disk.  In the process of dumping the
  data I inadvertently dumped two days to the same tape when messed up
  my tape pattern.  To fix that I decided to mark the corresponding
  unneed tape (107) as no-reuse.  After that Amanda insists on having a
  new tape, instead of the next one in line (108).  I have reset 107 to
  be reusable, but amanda wont go back and reuse it now either.

  Any thoughts on how I can fix this without messing with all of my
  tapes?

I would suggest that you solve this by choosing to stop worrying about
which tapes are used on which day.  Does that actually get you any
benefit?