Here is an example of a batch data management campaign to populate an empty Country field with the Inferred Country value. In this case I only wanted to populate the Country field if the inferred value isn't "Anonymous Proxy."
Populate Country with Inferred Country Value
If necessary you can use the ‘Add Choice’ logic in the Change Data Value flow step to change the Inferred Country value to a different value.
Run daily in the middle of the night.
Create the campaign as a trigger campaign if you need low latency. Here is an example of building a trigger campaign.