SmartList values "clean-up" without losing historical data

Summary:

Looking to update a SmartList value to remove people who are no longer working within the Organization without losing data on historical records.

Content (required):

I have a SmartList which is used as a list of "ApprovedBy" values which represents specific people within our Organization. This is primarily used for reporting purposes on specific records and does not drive any workflow functionality. As you may expect, occasionally an Approver will leave the organization and no longer be valid entry. I'm wondering if there is a way to remove one of these values from the SmartList without all the previous records that had this value associated to be updated to show just the "ID" value.