well main reason I want to use a script is because I don't think you can do texture overlays on a post-process volume and I really want to mess around film grain -etc this is a tutorial that talks about changing pp effect with code http://www.moddb.com/games/unreal-tournament-3/tutorials/unreal-learning-6-post-processing…
Granted I've just created a post-process volume and set it around the given area I wanted to modify, there might be a way to enable the volume under certain circumstances. I'll try to check it out and make sure but if I'm right you might just be able to create the effect and leave it disabled then enable it in script (3d…