Ability to delete DHCP lease

It would be useful to be able to delete a DHCP lease before its expiry. I use DHCP reservations for much of my network and use different sections of my subnet for different devices. If I use DHCP in the first instance (as I do not always know the MAC) and then convert it to a static (reservation) but change the address to a different one, it continues to allocate the old address until the lease runs out