The simple answer is 'no.' But if you're really bent on it, Apple documents the process of creating a new user and integrating the old user's files.
http://docs.info.apple.com/article.html?artnum=106824 (updated 2005 so i assume the process has not changed)
I believe this is targeted at OS X client, as a standalone. The process for an OpenDirectory account may differ.
Also, there is a utility called ChangeShortName that supposedly automates this process at www.danfrakes.com. I haven't run it and I believe it's intended for standalone OS X clients -- I have no idea what it'd do on a server. I think it's one of those "run at your own risk" things.