I used AFX to change the AF2 file so 01/19 would be closed for landings and 04/22 for takeoffs. The file is correctly modified but the behavior of the ATC doesn't change.
The problem is, Flight sim ignores the closing of a secondary end of a runway if the primary is open so, you can only close a whole runway, not just one end. At DCA, a solution might be using the star technique to enable all runways.
Have a look here:http://www.downloadcenter.scruffyduck.org.uk/
Under the "Tuturials/Airport Design" folder, you'll find a document named "Xwind Runway tutorial" which explains how to use the crosswind runways method.