[Zope] Extending ZClasses

How do I extend a ZClass? Overwrite general stuff that I want to personalize for my own site. Can I just create a new ZClass with my Product as the Base Class? and then create objects with the same ids. Will that do it? Then I'll have to create a ZClass with a different id and meta type and that will complicate things. I have the Beehive ebook about ZClasses but that didn't help. Cheers, Peter