If you're using the default SpoofGuard policy, it will automatically approve the first IP that the VM boots up with. It's called Trust on First Use. Then if VM changes its IP address or MAC, SpoofGuard will detect that and block the VM. That's the idea behind SpoofGuard, to prevent IP/MAC spoofing.
That said, what is the exact issue you're experiencing? If you delete a VM, SpoofGuard automatically clears it from its configuration. And if you then create a new VM, even with the same name, SpoofGuard will treat it as a new VM. So it shouldn't retain any old registrations.