Some old topic, but
kmk писал(а):
For example I add default_fov to menu and save, but after restarting the game it's back to default value.
It seems that you have this setting somewhere in userconfig.cfg (or in config that executed from userconfig.cfg). So after you press OK button in menu, setting is saved and then config.cfg is executed. This leads to that userconfig.cfg is also executed (there is line "exec userconfig.cfg" at the end of config.cfg). So your option is immediately overwritten.
I attached user.src file that some person gave to me (sorry, I forgot who).
It have default_fov option and it works.