There are several options, that is one, Andy outlined a couple more.  It
really depends on what you want to do with the data you have, if you need it
or not.  If they are really wanting to start over fresh then it sounds like
you don't need to keep the old data and can reclaim tape space, then the
idea of renaming nodes or filespaces would be the best, then you could
delete the older data later and reclaim tapes.  If you need to keep the old
data and just want a full backup of everything then you need to ask what
type of retention you need and should this affect the existing data.  You
can do the selective backups, change the mode to absolute, do an archive of
everything.  I have had to use all of these options before, it really
depends on what you need for the final outcome.

Ryan