I don't know what I can do to help, but that's how you change the rendering mode without launching the game, and it shouldn't change the rendering mode once you saved the config file properly and remain that way until the game is launched.
You will not be able to change rendering mode inside of the launcher that pops up, it's stuck on the selected rendering mode. You can only change it in the .cfg file or if you enter the game and change it in the options menu. So again, the launcher does not change your rendering mode.
What you set in the config file is what the game will launch in.