Without code changes, the only thing I can think of is to 1) hurt Barney with something activated by the player, like a
trigger_hurt
, so he retaliates, or 2) kill a scientist (with the "gag" flag on so he doesn't scream) with the same method and let Barney witness it, so he considers Gordon hostile.
Not sure if triggers will propagate the inflictor info correctly though.
If you don't mind changing the code, then it's a lot easier, either make a custom trigger to provoke a named Barney entity, or just change the relationship with the player to be hostile (
https://twhl.info/wiki/page/Monsters_Programming_-_Classifications_and_Relationships).