You can choose between normally open or normally closed type rain sensor, to select the logic (active high or active low).
If you want more than just on/off, then you would either have to modify the firmware or write an external script. Since many users have custom needs, it’s not possible to write the firmware that addresses everyone’s need. The whole point of this being an open-source product is to give users the power to modify the firmware themselves, to accommodate any custom needs they may have.