If a change has far flung consequences that aren’t obvious, the code is of poor quality. If the reasons for the decisions are non-obvious, the code is of poor quality. I’ve been bitten y assuming that people thought things through the first time too many times. If it’s not in the code base or documentation, I’m assuming that it was done for expedience. Not because they were dumb, but just because that part of the code base wasn’t important when it was written.