I think the main thing relevant to the coup was the Koi pond section. It had 2 distinct messages that I see:
1. Small changes have ripple effects that can change anything. We have already seen small changes, and these can cause ripples that mean nothing in the old timeline is guaranteed, coup included.
2. The fish adjust to his finger. Changes are adjusted to and accommodated: certain events are likely to recur. This has broader implications than just the COup, but with reference to the coup, it indicates that something along similar lines could still happen. This is further supported by the discussion at the end: both Shoju and Kachiko I read as sincerely rejecting the possibility for the moment, but both are aware that it could perhaps be done.