Is there a way to edit a review I wrote that's already been posted?

...but you need a good reason, such as you made a mistake about the services offered or you revealed information that you shouldn't have.  Contact TER support, tell them why you need to make the change and then they'll make your review editable.  But they will frown upon things like changing scores.

If you have a good reason to edit a review, admin may, I say again may, let you do it.  But you have to convince them that the reason why you want to edit the review is a good one.  Before it's posted, you have time to change things, but once it's posted, you have to appeal to admin to edit.  I did it once and they let me do it, but you never know.