[Zope] adding method to class after object creation

[Ruslan Spivak]

Hello.

Can anybody help me with the following question:
I havbe created zope/cmf product(e.g. LocalizedDocument) with class. 
User have created about 40 instances of that class in different places 
in zope tree. I need to add some methods to class, but how can i apply 
those changes(new methods) to already created objects? I have tried to 
add one field to class, after restarting zope  that field automagically 
appeared in already created objects(i made catalog search and tried to 
access that field from python script, it worked), but i don't understand 
how it works and if it's usual case or i need to do something more to 
add new features to already created objects when doing changes in the class.

Your help is very appreciated.
Thanks in advance.

Best regards,
Ruslan