Moderators can edit the posts.
I remember frodocooper edited many posts on mining board when he was a moderator.
Click
here to see an example of posts being edited by moderators.
Yes moderators can edit posts, but i think it is wrong for them to edit texts/content written by users, editing texts can lead to drama and a lot of people complaining that moderators changed their "idea" in their post. I can see that the mod in the link you posted used to edit posts when he was active, but as far as i can remember, i don't think i have seen active mods editing texts, or do they?