Is it possible to project a 2D rendered image back to its 3D model? I want to modify a 3D model in a particular way. Render images, modify these images (using a python program), and project these modifications back onto the texture. Is this possible or not?
Yes it is possible and called projection painting. CGMatter has tutorials on this topic that should get you started. Blender 2.8 Texture extraction projection painting (part 1) and Blender 2.8 3D Object removal projection painting (part 3)