@gp-sm-het-maas:~$ maas 19-root subnet  update cidr:192.168.24.0/23 vid=10
Success.
Machine-readable output follows:
{
    "dns_servers": [],
    "name": "openstack-external",
    "space": "default",
    "vlan": {
        "name": "untagged",
        "vid": 0,
        "mtu": 1500,
        "fabric": "maas-external",
        "id": 5001,
        "resource_uri": "/MAAS/api/1.0/vlans/5001/"
    },
    "gateway_ip": "192.168.24.1",
    "cidr": "192.168.24.0/23",
    "id": 2,
    "resource_uri": "/MAAS/api/1.0/subnets/2/"
}