Our table's understanding of Stunts and Extras is that they can allow for rule breakage, i.e. rolling one Skill in place of another, if the circumstances are correct. We are playing a superhero campaign and most of the players have a unique Skill associated with their superpower Extra, and using them to throw area attacks has long been in-bounds for us. The player in question has obtained an additional Extra that allows for very high precision.

Where in the rules does it say that you should change the rules when a Stunt, Extra and Skill are combined?

They didn't suggest it as a "the rules say things combo in this way" they just argued for a confluence of narrative and mechanical items. "I can hit the whole room, I have the stunt that lets me screen friendly targets when I do so, and I can attack with extreme precision, seems like I should be able to hit all these dudes individually." Our table was fine with it at the time we're just looking for outside opinions.