JSON format documents require \n for new paragraph and // when using adding special characters. If Edit Value in MongoChef would allow you to enter string information much like CDATA in XML then SET VALUE should add in the relevant codes required by JSON document when it writes. When viewing and editing the value, the codes should disappear and it should simply show special characters and carriage returns.
This would be a good solution to edit content for on-line products in a product catalogue, for example.