As an aside, although it makes sense to make things uneditable once approved, I would like to point out that constructive criticism often comes after the fact and also that sometimes I notice things (or they are brought to my attention) that require minor adjustment in my approved designs, such as improvements to text flow or a more readable formatting.
I would suggest that the 'approved' section be allowed editing and replies, but not new topics by general users, as a potential response to these issues.
