Greylisting reject code 452

I noticed that the returned DCC greylisting error code is 452. According 
to what I have been reading recently there are many more greylist broken 
MTAs out there than if code 451 were chosen. So my questions are why was 
code 452 choosen and can I change it to 451 to see if it works better 
(in the sense of not needing as large a whitelist)?

-- 
Paul (ganci@nurdog.com)