If I have an award booking, can I call BA and have them somehow "convert" it to an MFU?

Alternatively, how easy would it be for me to accomplish what I want manually via ba.com? In other words: How is award inventory handled when an award booking is cancelled - is it automatically and immediately made available for new bookings so I can quickly grab the seats in a fresh MFU booking, or is there some indeterminate waiting period that would make it hard to avoid losing my seats to someone else?