I want to create a pseudo 3D object, e.g. six sprites for each face of a cube that represents a bus. I then want to take this object and render or generate an output based on rotation input. As an example, if the bus is turning at an intersection, it should generate or render a pixel art object for each frame, modifying the asset as the bus turns. The asset should look as if it was hand drawn (no shrunk/stretched pixels)

Other restrictions:

• The camera POV is fixed at isometric (infinite horizon, lines to not converge/they do remain parallel).
• My game is 2D, so I'll be generating the assets on the fly.
• Sprytile/Crocotile is not what I'm going for

Is their a library or method for creating this this behavior?

No, can't be done. The only way to create pixel art is to actually hand-draw it.

The typical approach to avoid traditional 3D rendering is creating sprites for a variety of viewing angles and lighting conditions ahead of time, often by carefully rendering 3D models at low resolution and applying some combination of fancy shaders, postprocessing and manual editing.

Why can't you do that, and you want to render your sprites on the fly instead? On the other hand, if you want quality realtime rendering, what's the problem with regular 3D models, which wouldn't require too much detail?

Why do you want your models to be “pseudo 3D”? A textured box can look like primitive 3D art, not like good 3D art (which requires correct shapes) or good sprites (which require flattened billboards instead of oblique box faces).