@wendypalmer @strangeseawolf @Nichelle
"I’d most like to write a book as usual, then click a button and have every pronoun switch, and see how that affects the story."
Character tags (little bits of description or telling action attributed to the character) are subtle bits of subtext that we use to make a story flow transparently. In my /Mask/ story, for example, the character "wipes unexpected hot tears" after being shot down. Feminine, right? Wrong. Men will react privately, or unconsciously, or if they haven't bought into guy-culture, easily. But without pronouns and gender subtext-ing, the statement becomes fodder for the reader deciding not only "what" but "does it actually matter?" My removal of the few gendering words didn't change the character, except in the reader's mind. Yep. Caveat, very short story.
My bet is switching "she" to "he" globally will be less jarring than vice-versa (make-up and dresses notwithstanding, maybe.) These days masculine behavior in women is much more accepted still than the other way around. In the end, your result depends on how you write your characters. I-POV makes a big difference, of course.