[Zope] Moving Property sheets between ZClases

Hello Zopistas - I am not sure if this question is for the Zope-dev or for here ... I am in the process of creating my first ZClass. I have created a property sheet with about 20-30 properties. Now I have realized that I needed to inherit from one of the base classes. I could not find a way to add the desired base class to the already existing ZClass (something I expected), and I could not find a way to copy the property sheet from the old ZClass to the new one (which I did not expect). Any ideas? Also if I have a bunch of python classes that are not a product in themselves but are going to be used by the ZClass, where is the right place to add them in the Zope tree. Under Shared? Thanks Pavlos