What is that plastic piece that extends the light from the PCB to the outside of the case called? Can it be 3d printed?
A "light pipe". I'm sure you could 3D print some sort of light pipe from transparent filament but likely some materials will make better light pipes due to their optical properties and also the printing process may not produce a high level of transparency. I know acrylic can be used for this purpose so laser cutting may be a better manufacturing method.
Trying to 3D print them would be an excerise in futility. Why fuss with trying to re-invent the wheel?
Hi
3D prinitng will not produce a light pipe.
The 3D printer prints in layers, these layers will provide changes in refractive index and scatter any light you try to emit down it.
Tom... 
rylo:
What is that plastic piece that extends the light from the PCB to the outside of the case called? Can it be 3d printed?
Not sure what you're on about.
Do you want a LED on the outside of a case that reacts like the LED on the PCB?
Leo..