Twitter – Hierarchical connection of Twitter subaccounts possible

You could also try twittergadget.com. When you are at home you can set up an account with this site and it authenticates with Twitter. At work, it uses different URL's and you can use/manage your Twitter without actually accessing Twitter.com

You'd need to have a third name as you'll need to do this:

1. rename @mike_me to @somethingrandom
2. rename @mike_and_long_name to @mike_me
3. rename @somethingrandom to @mike_and_long_name

From what I remember when other users have changed their Username your followers will still be following the accounts they were originally. So if @Joe is following @mike_and_long_name and @Bill is following @mike_me once you have completed the swap @Joe will be following @mike_me and @Bill will be following @mike_and_long_name.

It would be sensible to warn your followers that the name swap was about to happen so that they don't unfollow because they now think that they are following the wrong person.