how to handle a polarity change deep inside the sub narrative tree?

A totally idiosyncratic question, but the answer is theoretical, and postulates that a narrative can have only a positive value or negative value. You are not waiting for an ambiguous good/bad to occur but are operating with a current one.
So the answer to the question is: whenever a deep polarity change occurs, the whole evolving narrative should get its polarity changed as well.
Update: It is particularly interesting to suppose a collection of alternative interpretations that widens and narrows on the way through a text but with one component - the value - being shared by all the alternatives. This 'value' is always current and is not projected as a possible future.