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