You can! Pixy will ship with a 75-degree field of view lens, which is great for robotics applications, but your application may need something different, perhaps something that can see distant objects better (longer focal length) or see more objects (wider field of view and shorter focal length). Or a lens without an IR-cut filter, so that Pixy has the best IR response.
Pixy uses a standard M12 lens. These are available through several vendors. Here's an example (there are others):
We may end up selling different lens options with Pixy, but at the very least, we'll create a list of lenses that work well with Pixy and where to purchase.