Customized policy fields for Amavid-new

[admin at goldenpages.ua]

Hi list! Everyone saw an example policy for amavisd-new , so my 
questions are:
Can I add my own fields to this table 
(message_size_limit,bounce_message, etc)
Will Amavisd understand customized fields, or it's impossible without 
code  modification ( developing plugins,scripts,sources modification) ?

Thanks in advance, Sergey Kazak.