There's not much in the way of direction when it comes to analog audio signals. For output, you're driving the coil with some current. For input, you're reading current from the coil. This particular chip supports both on the same wires, you just have to tell it which one you want.

> Is reassigning port direction possible even when there's just one physical plug?

Yes. I have an Acer Vostro laptop and whenever I plug anything into it, Windows asks if it's input (mic) or output (speakers) device.

The chip in my MacBookPro11,5 is identified only as "Intel High Definition Audio". I couldn't find any additional info on the specific chipset.