How to update number with rules when importing

Hi everyone,

I am trying to update the number during importing. For example, for 2021, I have actual data from Jan to June and forecast data from July to Dec. the target module is on yearly basic, therefore I would need to combine both actual and forecast for 2021. I want to do the import in two separate action: 1. import the actual and 2. import the forecast. However, when doing this, the number is only showing actual data and not the forecast. Is there anyway that I can add the forecast number to the imported actual?

Due to some requirements/reasons, I can not sum them up before importing. Any suggest are welcome. Thank you.