There can be multiple such plugins installed at the same time, then the user interface allows to switch between them easily. The Standard AI packed with the game is a normal plugin and could even be removed from the installed AI pool. 
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<p>
In addition to a simple AI replacement, the "Free Player Setup" enables the following scenarios:
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<li>
Play games against different AIs at the same time. There can be up to 8 different AIs playing in one game, controlling up to 14 nations.
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<li>
Watch