You don't need to learn C#. You would need to learn TorqueScript, which is the language used to modify the game (any Torque game, really). Player turning is handled by global variables that are attached to yaw/pitch/roll. The object used for controlling those via mouse is called an ActionMap. Unless it was specifically renamed by the dev team, the default ActionMap instantiation is called moveMap:
This is usually set up in default.bind.cs. When you run the game for the first time, it saves your configuration to a script called config.cs. This is, of course, all coming from memory. I would have to shake off my Sunday laziness in order to go upstairs to my PC and check the files. The point I'm getting at is you want to find the function that binds the mouse axis to the yaw/pitch/roll global variables, then create a hotkey binding to manipulate that variable.