you can try using just this (delete the other comments)
[Weather]
UseWeatherFile=False
WeatherCanBeLive=True
thats what i edit in Bush Trips to get Live weather, it allows you to open the weather tab from the toiolbar once your ingame and auto sets it to live when you start
never tried it with a saved game .flt other than those, i believe it just makes it ignore that ‘saved’
weather data