I have managed to do this now by changing a line in the script file chatclient.js (in the scripts folder). I then call my embedded chat page with a couple of parameters:
For example:
embed.aspx?room=1&UserName=Steve
Then in chatclient.js
I have altered the code in Function Connect(placename) so that the following line
cookie.GuestName=chatclient.guestname;
now reads as
cookie.GuestName=location.href.substring(9+location.href.indexOf('UserName='));
This results in the User name appearing as Steve. Obviously you can provide any alternate user name instead of my 'Steve' example.
Hope that this helps other people wishing to change the name too.
Gerard