I made some changes to camera.xml files of all ingame cars,
so now you are able to change FOV for Dash Cam with ingame slider.
This won't affect any other cam, they will act as before (if you dont have some cam mods already installed), and all cams (Bonnet, Bumper, Dash, and Head cam) will have same FOV.
Thought it would be useful for someone.
1. Extract "cars" folder to your "DiRT Rally" folder and overwrite. (Backup your files first)
2. Make changes to FOV in Profile/Game Preferences/Camera Field of View (1st screenshot)
3. Enjoy ;-)
P.S. Use at your own risk.