Create new family from existing

Hello. I want to implement such feature:

1. User places some component family instance on the drawing
2. Then user selects it.
3. Program should extract the family object of the selected instance
4. Program should create the copy of the extracted family, modify some parameter of the family (create new family on the base of existing), and place instance of newly created family on the drawing

I do not know how to create in-memory clone of the source family object and save it in current project (or separate .rfa file). How can I implement this?