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From Paizo's own:
"The Most Important Rule
The rules presented are here to help you breathe life into your characters and the world they explore. While they are designed to make your game easy and exciting, you might find that some of them do not suit the style of play that your gaming group enjoys. Remember that these rules are yours. You can change them to fit your needs. Most Game Masters have a number of “house rules” that they use in their games. The Game Master and players should always discuss any rules changes to make sure that everyone understands how the game will be played. Although the Game Master is the final arbiter of the rules, the Pathfinder RPG is a shared experience, and all of the players should contribute their thoughts when the rules are in doubt."
I'm definitely with PSY850 for houseruling in mid campaign especially when it comes to new material which oh by the way comes out every month. so I instituted a rule of when a campaign starts you can only use existing material and can never use anything new that comes out during the campaign.
It's not the GM's job to know how every feat and archetype work in every single circumstance and it's not the player's job to act like a CO-GM.
A GM in my book only needs to know the basics of the core rulebook and a desire to tell a great story.. the rest is just so much noise.