I believe you can, but the only way I think you can do it is through bulk uploading via an excel or csv file. I've actually been meaning to do this as well for a few thousand keywords I have. I figure MSN is cheap enough where I can go with the throw enough shit against the wall and see what sticks theory.
You can change it after the order is accepted.
Go to the campaign then the ad with the keywords. Choose to edit ad. Then you can change title / description / url for each keyword, and it will make a new ad out of that one.