Management network and default gateway

Hi,

After the initial setup (via serial cable) we've set the default gateway on iSCSI network. Ip address is set for management interface on management network as well. Now we want to access management port from different network. 

Actually we don't really need dg on iscsi network as there will be no replication etc to another network. So if I try to change dg on GUI it doesn't allow me to change it. Can I change dg on cli or add new routings for management network?

Thanks,