I've also posted this in the Feature request list.
When an interface is configured as a DHCP Client it has the "Renew" button. I'd like to see the addition of a "Release" button that performs a proper DHCP_RELEASE such as performed by "dhcpcd -k ".
Verizon FiOS requires that the DHCP address be released, otherwise a different device (different MAC) cannot receive a new DHCP assigned IP until the previous lease expires (2 hour leases on FiOS). Their Actiontec MI424WR routers have it.
Please add the button for DHCP Release.