isi networks modify pool --name=subnet_name:pool_name  --sc-suspend-node=1  suspends node 1 from being used by SmartConnect
Community,   There is supposed to be a command that you can use to disable future SMB connections a node, but the trick is that the command doesn't disconnection current SMB users from the node.  I believe its a isi network command but don't know what the correct triggers would be.  
Isilon - Disable new SMB connections to node