Any way to delete MAC Address

We have added all of our MAC addresses across the company and would like to be able to remove old MAC addresses from the system after they have been retired.  Is there anyway to remove the MAC address from the database and white list?

I have created a resource that lists MAC addresses that have not been seen on the network in over 30 days.  This way, when a device (say VM Server) is removed/retired we can also remove it from our white list and remove it from UDT.

Is this possible?  How long will a MAC address stay in the database past its "last seen" date?

Thanks,

Mark S.