Changing it in the CSV is simple. You can do it in a text editor or a spreadsheet application.
Depending on what else you have in the database, you can do an update to change from "Completed" to "Yes" and "In Progress" to "No".
If you don't want to do that, you can do it in the SQL that gets the data from the original database with a CASE statement. Such as:
Code:
SELECT Title, CASE Status WHEN 'Complete' THEN 'Yes' ELSE 'No' END as Status
FROM thetable
Otherwise, as BR suggests, import it into another column and modify things afterwards.