Developer Characters

I was wondering - would it be possible to make it so that if you enter a certain name when you join a server, you are prompted with a password window, and if you have the password, you get to use a special character?

This would be for admins. Example: If you enter the name 'DarkOne', a PASSWORD prompt screen comes up. If you enter the password 'BlackStar', you get to play as 'Vista'.

I am a horrible programmer, so can anyone tell me how to do this?