This is pretty easy. You need bot events.
Spawn a Standard Bot and give it a Renderman Avatar. Look at it and type /getid
Remember the object ID
Now in the console type: findclientbyname(NameHere).setcontrolobject(OBJECTID);
Replace OBJECTID with the ID you remembered, and NameHere with your name
Now you should be controlling Renderman, but how do you speak as him? Easy.
Messageall('',"<color:ffff00>Renderman<color:ffffff>:");
After <color:ffffff>: add a spacebar, then type your message.
Example: Messageall('',"<color:ffff00>Renderman<color:ffffff>: I AM RENDERMAN. I WILL KILL YOU.");
You are now Renderman. Enjoy!