What you basically need to do is export the zpool using the shell command line (not on the web interface).
The commands a fairly simple.
zpool export [current zpool name here]
zpool import [current zpool name here][space here][new zpool name here]
Example:
zpool export volume0
zpool import volume0 volume1
Keep in mind that afterwards, at least I had to do it, to detach the volumes (zpools) from the system (DON’T CHECK THE OPTION TO ERASE DATA).
Reboot.
Auto-import volumes (zpools).
And bingo you have the volumes back with the new names and all of your data kept intact!
More Information [Detailed]:
http://docs.huihoo.com/opensolaris/solaris-zfs-administration-guide/html/ch04s06.html
http://doc.freenas.org/index.php/Volumes [Detach Volume Section]
http://prefetch.net/blog/index.php/2006/11/15/renaming-a-zfs-pool/
http://forums.freenas.org/threads/renaming-volume-with-data-already-in-it.13061/