cinderclient support manage and unmanage snapshot by commands below:
usage: cinder snapshot-manage [--id-type <id-type>] [--name <name>]
                                  [--descriptio n <description>]
                                  [--metadata [<key=value> [<key=value> ...]]]
                                  <volume> <identifier>
usage: cinder snapshot-unmanage <snapshot>

But OSC does not support these now.