Am I right by asumming, that if they would play another game (AlphaGo black and Lee Sedol white), that Lee Sedol could pressure AlphaGo into makeing the same mistake again?
This is an interesting question - if Lee Sedol simply replays the game exactly, does he repeat a win?
I think the answer would be most likely not - the monte carlo tree search is randomized so AlphaGo's responses to Sedol may not be exactly the same, requiring Sedol to not be able to repeat the exact same play.
They stated before game 3 that AG had been locked down a while before these games to test the code for bugs and issues. I also think they don't want some of the implications associated with DeepBlue where people modified code even during the games.