Yes it is! C:\m-r-software\Omsi\Weather\ICAO.txt
Here do you add the ICAO to the closest airport to you.
Example. Molde Aro. Is my airport. The ICAO is ENML. I then add the name
ENML - Molde
LIRF - Rome
Hope you are in to aircrafts as i am, then this will be a peace of cake!
Just ask me if you need help finding a ICAO! Or just use google!