I am pleased to report you can revise your review even after it has been posted. It will be checked by management before it is reposted as you want it, but if you decide to delete information about the story that gave too much information about the plot (as happened to me recently) or if there are words you didn't spell exactly the way you wanted or a stray comma or any other change you want, even to change or delete numerical scores, all you have to do is go to your review site up near the top of the front page, select the review you want to amend, make the changes, and hit the publish button. Management will look over the revised review and if they approve, the review is changed. No it doesn't start over at the top of the front page, but it is still associated with the story you reviewed.
If you get an author's comment you feel needs to be addressed, you can adjust your review to do so, and your initial impression does not need to follow that story around forever.