Suggested new feature

In the Address book, make it possible to duplicate a list with a new name that one could then add or subtract members.

By ‘list’ do you mean address book or mailing list? To duplicate an address book, create a new address book, name it and close it, then select the contacts in the source book and copy them to the target book by drag and drop onto the book icon, while holding Ctrl. With mailing lists, copy from one list to another by drag and drop.