Use a symlink?
/home/username/symlink -> /home/username/user-file
Then all you have to do is update the symlink to point to different files and not have to edit the .htaccess file anymore. Uh, as if it would be much harder to just rewrite the user file in the first place, but oh well. Probably depends on how often you need to switch files or update the user list; updating the symlink might be more atomic…uhm, haven’t checked yet if a symlink will work (perhaps restricted for security reasons)
Perl / MySQL / HTML+CSS