Another way to delete a targetGeom channel in the interface is to select the channel in the Hierarchy Editor then hit the keyboard Delete key. This woks from at least P4 up.

You can use a whole pz3 in a pz2 or cr2, but if you load it into an existing scene it may have bad effects on the lights, if lights with the same name exist in both scene and pz3. I would sugest deleting the lights either from the scene or from the pz3 first.