Maybe... an anagram or something...
Not the Macbeth quote, but let's break it down.
Proper words mentioned that could be game related:
blood, stones, trees, augurs (see the future or observing and interpreting signs and omens), relations, maggot-pies and choughs and rooks (birds: magpie, red footed crow, black crow), secretest, man, and night.
Now it goes without saying, if a rockstar used this quote from Shakespeare's Macbeth then Shakespeare was not involved since he died hundreds of years ago. All the game maker has to do is make shure we have all those things to find inside the game. There is plenty of blood, rocks, trees and men in GTA. All the birds mentioned are black and I have seen brown birds and white birds but no black birds in the game. We are also given a time of night.
Damn, I hate to be such a wet blanket. But I don't believe you will find anything this way. As I said before, I am not looking for a magic switch but some type of hidden code puzzle.
Thanks for the assist, I can appreciate your point of view, but we will keep looking under the rocks. Who knows, maybe the magic switch got removed when they took out the other stuff or before it ever hit the shelf. So then you could be partially right. Where is this bloody cabin?