[Zope-CMF] Changing permissions on CMF types

[Michael LaPera]

I am using Plone and I have a custom portal_type "MailMessage" (a la 
CMFMailn)  with the actions ("view", "send", "redirect", "forward", 
"reply").  When an object is added I would like only the actions "view" 
and "send" to be available, but after a member sends the email I want to 
hide the "send" action and make available the "redirect" and "forward" 
actions.

I can, sort of, reproduce this by going to 
"/MyPortal/portal_type/MailMesage/Actions" and setting the permissions 
to "(none)" in order to hide the action and then setting it back to 
"View" or "Modify portal content" to show it again.
How do I reproduce this show/hide action permissions in Python?  I know 
it probably has something to do with "AccessControl.ClassSecurityInfo", 
but I just can't seem to put it all together...