I dont really believe editing the caption automatically kills the reach. I've changed typo on posts before and nothing bad happened. Other times, it still flop but who even knows whether it's the algorithm or people just ignored the post. Social media don't even has one fixed formula again. Today everything is working well, the next day it's a different story entirely. I think if it's a little small correction, edit it and move on. But if you want to completely change the message after you have had enough engagement, that can confuse people.