I propose to add a new method in JCodeModel : copy().
This method returns a new CopiedModel that contains recursive copy of all the elements of the parent model.
This CopiedModel also allows to translate the elements of the parent model into its own elements.

This method could be used with the preprocessors : instead of working on the original model, processors would be applied on the copy. If no processor is used, then no copy is done.

Working on it.