I am creating a incident template and I want to change the site field depending on which region is chosen in a region field. 

eg. 

If a region is set to "NCA" then the site should change to "New York"

But the field rules do not seem to change this/ nor any custom script  - eventhough the same setup works for other fields. 

Is it not possible to change the site field with rules?  

best regards 

Max