You can change the encryption key associated share at any time, even while it is in use by client systems. To change a key for a share without changing the parent project, use the following procedure:
hostname:shares default> select fs-1
hostname:shares default/fs-1> get keyname
keyname = MyFirstKey
hostname:shares default/fs-1> set keyname=MySecondKey
keyname = MySecondKey (uncommitted)
hostname: shares default/fs-1> commit.
shares default/fs-1> get keyname
keyname = MySecondKey