Hi! And welcome to the world of RunUO, player run shards!
What I think that you are going to want to do here, is go into the script support forums.
http://www.forums.runuo.com/forumdisplay.php?f=16
Ask about this there. Post the script that you are using now, in code tags which are [.code] the script code [./code] (without the dots in there, I had to put those in to let you see the code.) by opening the script in notepad, then edit>Select all, Edit>copy and then paste the script inside the code tags.
In there, they can help you along with changing that script if you need it. what you are going to want to do, is start to make changes to it, where it makes the changes to that characters name.
Edit it so that it sends a message, like "That name is already taken, please select another" Or whatever you want it to say, rather than changing the character's name.
I'm sorry that I cant be more help to you than that. But I am REALLY rusty at doing scripts, and I am still using an older version of the server that may handle things differently than your's does.