Option to disable update existing records in import

We would like to have a little more influence on the import actions. The import now follows the allowed actions. What means that if you cannot insert it will only update and if you cannot update it will only insert. I would like to be able to have a custom setting for the import.

For example we have a page where the individual records may be edited, in the form. But new records are mostly imported via the import function. Sometimes people accidentally do an export and copy some records but they forget to remove the id. What happens then is that the record that should have been added gets updated instead. (completely logical since it is using that key) To avoid this we would like to disable the update existing rows functionality for imports.