what in the world would stop you from playing with OS on a normal map?.. If there is no OS tags in the map, then the only added features will be stuff like shader_enviroment showing their bump/normal maps (even on scenery and such (OS shader_model can have bump/normal maps too now, but that wouldn't be in a regular map)) aswell as postprocessing linked in your configuration file (motion blur by default, you can add more)

And to play a OS map without OS installed, if there is OS scripts, you must pad the script commands so they wont execute on nonOS computers. If the OS scripts execute for any reason on a computer without OS, it WILL exception.