Why interfering and not letting your kid develop his own ways? Answering "How are you?" in detail sounds to me as a fantastic trait of his personality.
When I was 7-years old I stopped calling my parents mom and dad and switched over to calling them by their names. I just couldn't understand the logic of other people call them one thing and me calling the something else. Happily nobody tried to "correct" me according to social rules, and still today it wouldn't cross my mind to call my mother 'mother'!
I call my mother "Mom" and my father "Norman". I'm not sure why; all I know is that I started when was small.
I've seen an article on LW about Santa Claus and most people were very keen on not lying to their kids (and I agree). I have a little kid who is generally quite truthful, innocent enough not to lie in most cases. I noticed recently that when someone asks him, "How are you", he usually answers in detail because, well, you asked, didn't you? When I was a teenager I hated people who lied and I tended to ignore these unwritten social rules to the extent I could. I.e. I didn't ask if I didn't want to know and people thought I was rude. So, my question is, should I teach him to lie upon these occasions?
More broadly, I was thinking, why am I committed to being truthful, in general? I guess because I would hate to be lied to myself. This is a kind of magical thinking maybe, or maybe it's a part of the social contract. This sort of lying in fact promotes the social well-being because to answer truthfully creates an unwelcome burden on my interlocutor who asked out of politeness and is not in truth interested. But it still feels wrong to lie. Even more wrong to teach your kid to do so.