Click on Athletes from the Main Menu Bar and then the Add Athlete or Edit Athlete button. Click on the Status pull down arrow and click on "Foreign" to declare that Athlete as a Foreign Athlete. The status for that athlete will allow you to restrict Team Scoring or Seeding in the A-Finals of a Championship meet. Click here to see how to Restrict Team Scoring from the Entry/Scoring Preferences menu.
When you Export Results at the completion of the meet, you also have the option to "exclude" foreign athletes.