[Zope] Creating properties in python products

Hi, I have developed some custom products in python and this products has their own properties. Later I need to creat new basic properties. The objects with only the initial basic properties acquire the new properties but objects tha has other properties (created in the management interface) don´t. And because in this objects the other properties has the same name that the new basic properties ever if I delete the other properties I can´t create (in the management interface) an propertie with the same name tha the propertie defined in the python product (but no propertie with this name are show in the management interface). I am using Zope 2.3.3. Thanks, Georges Baladi