Is that StackOverflow policy officially in writing somewhere? I had one of my answers edited by a mod not too long ago without any warning. Wasn't too happy about it.
See the itemization of reasons to edit a post for. It also explicitly mentions that the meaning of the post may not be changed. You can, as the owner, also always roll back edits. Another option is to take it to the meta site and voice your complaint. One of the reject reasons in the review queue (note that moderator's edits don't go through the review queue) is if the edit changes the meaning of the post; the edit system is really meant (as the page says) for fixing typos and on occasion updating/adding information like if the post became outdated or to consolidate info from comments.
Everyone can also see the revisions of any (non-deleted) answers and questions, so if someone changed the meaning, it clearly says "person x edited this post" (right next to the original author's name) and you can click that link and see who actually said what.
Editing of answers is fine - by anybody, not just mods. That's because there's a clearly shown "edited" section displayed at the bottom of the answer, along with the editor's name, right next to the "answered" section showing the original author's name, indicating to anyone who reads the answer that it's a jointly-authored post that isn't entirely the original author's work. You can also look at the revision history to see exactly who wrote what. There's no false attribution there.
Comments don't have this history or indication of being edited by a third party, though, which is why only moderators have the power to edit them and most such edits are considered unacceptable and banned by policy.
See the itemization of reasons to edit a post for. It also explicitly mentions that the meaning of the post may not be changed. You can, as the owner, also always roll back edits. Another option is to take it to the meta site and voice your complaint. One of the reject reasons in the review queue (note that moderator's edits don't go through the review queue) is if the edit changes the meaning of the post; the edit system is really meant (as the page says) for fixing typos and on occasion updating/adding information like if the post became outdated or to consolidate info from comments.
Everyone can also see the revisions of any (non-deleted) answers and questions, so if someone changed the meaning, it clearly says "person x edited this post" (right next to the original author's name) and you can click that link and see who actually said what.