Updating CSV Files

Hi! I have a macro that essentially loops through and grabs all of the store names at a shopping center and saves them to a CSV. I want to run it every month, but when I do run it it just appends the new list to the same csv with all of the repeat stores. Is there a way to update the csv with just the unique values? Or compare it to the last csv file and create a list of only the unique entries from this second execution?

For information on how to update or overwrite a value in a CSV file see How to mark a row in a CSV line as processed? - #3 by TechSupport