In case you missed it, Mastodon now lets you edit posts ?
You can edit any post you've made, and it will send a notification to people who have already interacted with it to prevent any hijinks or shenanigans. It also lets people see the previous versions.
You can access it through some third party apps and your server's website. The iPhone/iPad app Toot! has it for example.
(The official app doesn't yet support it, so it's another good reason to check out third party apps.)