Steve,

The best way would be to use "move data".  You can change the destination
for the current copygroup to new storage pool before you start moving data.
This will give you enough time to move your data while the new backups are
sent
directly to new storagepool.
You can also you "nextpool" but you might get in loop of data coming in to
old
pool and then migrated to new pool, if you have lot of data.