Custom field to candidates

Summary

Adding a custom field to all the candidate in particular location

Content

Team,

Our HR recently requested to add a custom filed like "Alumni" "Ex contingent worker" "contingent worker" "General Application"  "Prospect" etc.. so they can identify the candidate by searching. We have total of 10000+ candidate, which includes close to 2000+ we can purse future. I would like to add a "General Application" status to all the candidate first and then change the status to 2000 candidate later. My questions is how can I mass tag the custom value "General Application" to the candidate who are in Country USA. Let me know if you have any better suggestion to make this happen.