>I have a class library with a combobox that I've customized by adding additional properties and methods. Now I want to use it as a starting point for another combobox class. Can I duplicate it without having to manually rebuild the entire thing as a new class? I thought that the Class Browser might do it but I don't see anything there.

You want to have a copy of the class in this library or create a new class based on this class?

If the former, open this and another classlibs in the project, drag the class to another library, rename, drag back and delete from the other library.