Timboli: My view, is that you should be able to add to your review, but not change it. That would give greater understanding, especially where you have later changed your mind for whatever reason.
No sense in trying to rewrite history.
Reviews should have an expiry date anyway, like 5 maybe 10 years (that is long is it?)
After this time, let it be automatically archived in a ...in a... in a
Reviews Archive! Yes!
until game has not changed, than no reason to do this.
as for editing reviews: better to add a new one and archive old one in a safe place
Games are getting updates, DLC`s patches and additional localizations etc.
Games are not paintings or movies,
they (I like games) are changing, so the reviews should.
Vote +1 for Reviews Archive here
https://www.gog.com/wishlist/site/reviews_archive