Is it possible with some script in the CS to change the percentages of the region weather types permanently after completing a quest or reaching a specific quest stage.

For example BravilWeatherRegion is originally:
Clear 35
Cloudy30
....
Fog 5

And I want to change it to for example this after completing quest x, or reaching quest stage y in quest x:
Clear 70
Cloudy 10
...
Fog 0