[rt-users] Prevent requestor from changing custom field values after ticket creation

[Jeff Ehrenberg]

I would like for users to be able to create tickets by email that
contain custom fileds.  I am able to get the fields populated using
RT::Extension::CommandByMail and Filter::TakeAction.  Once the ticket
is created I only want the ticket owners to be able to modify any of
the custom field values.  Is this possible?  It seems that if I don't
give neough permission then the fields will not get populated by the
email.