Yes but that is always a balancing act if you want to make any change at all since users can theoretically depend on any possible implementation detail or even on outright bugs.
Correct. It's always a balancing act. That means hard rules like "we will do any change which doesn't technically break any promises explicitly made in the documentation in a patch release" aren't appropriate, it's always a value judgement (and sometimes you get it wrong and revert the change once you realize that people were affected more than expected, as happened in the case of curl).