Just as a disclaimer to the movie Six Degrees of Separation, just keep in mind that it is different from three other interpretations: the play by Guare, the true story about Hampton, and the actual theory by Karinthy. Due to your question, you are limiting yourself then to the cultural codes and the setting of the movie as opposed to the other aspects of the true story. This might have a bearing on the heuristics (a quick answer through experience as opposed to research) for your subjectivity analysis.
This being said, let's reverse your question a bit in order to analyze the setting, which is the "context (time/place)" which is how setting is referred to in literature. This must be done first in order to determine the "customs/norms/cultural codes" of that setting. Quite simply, the setting is the Upper East Side of Manhattan in the New York City of the 1990s.
That setting is very important to the "customs/norms/cultural codes" that can be found in the movie. These are the "customs/norms/cultural codes" of the Upper East Side of Manhattan in the New York City at the time. Let's take a closer look at them. It's a custom of the rich not only to procure famous art pieces, of which the Kittredges have a famous piece by Kandinsky, but also to display them for further patrons. This is the way the investor Geoffrey Miller comes into play. It is an unspoken custom for the rich and organic of the Upper East Side to show compassion to the less fortunate. Paul, of course, preys upon this. The fact that Paul is an African American also plays into the cultural code of binaries as seen here:
The ... critique of binary oppositions ... [argues] that the perceived binary dichotomy between man/woman, civilized/uncivilized, and white/black have perpetuated and legitimized Western power structures favoring "civilized white men."
As a greater irony, it is interesting that another cultural norm comes out near the end of the movie in that the Kittredges feel called to "share" their story in the form of gossip with other members of the Upper East Side. In this way, they learn of the notoriety of Paul who has now become legend at the cocktail parties of the artsy rich of New York City.