To alter a player's vision statuses, we can use "Run AI Script" action "Turn ON/OFF Shared Vision for Player X". The action may operate opposite of how you might imagine, however- turning ON/OFF vision with a player does not change the trigger owner's status with that player, but rather turns on or off that player's shared vision with you, the trigger owner.

For instance, if one wanted to give Player 2's vision to Player 1, we would Run the Ai Script "Turn ON Shared Vision for Player 2" in a trigger owned by player 1. After this trigger owned by P1 runs, he will be able to see all of Player 2's units, and cloaked units owned by Player 2. One should note, however, that it takes a moment for this change to be taken into effect.

Another application and possibility of changing vision statuses is to turn OFF shared vision with the player that owns the trigger. IE Player 1 would run the action 'Execute AI Script 'Turn OFF Shared Vision for Player 1'. This would remove Player 1's ability to receive vision from his own units. If, however, his units are visible to him (by being within vision of a player he receives vision from) the units will always be detected for him. For example, Player 1 could not own a Dark Templar and see the area its in but have it be cloaked. Either P1 can not see the whole area, or he can see the area AND his own cloaked units.