I can feel your pain, I, too, write (don't worry, my language of choice is not English). And I usually pick the words I use carefully and with reason. There are minimal but very important differences and my readers usually enjoy my choice of words because that choice by itself often has a meaning.
In this particular case I don't think that the robot would change words for ones of similar meaning like a badly done thesaurus on steroids. Rather, I'd expect them to add blanks (like, say, putting down two or three spaces between words instead of the usual one), omit a period at the end of a paragraph (where the average reader would probably not even miss it) or introduce subtle spelling mistakes (which is more easily done in languages that use diacritics with minimal impact on word spelling). My bet would be on the introduction of trailing whitespace characters or similar "invisible" things that the average reader would most likely not even notice.