I can confirm that the post process effects are captured in both left and right images with the aforementioned GetViewState() changes. But there are certain issues with noise and banding. This image has been captured with quality = improved setting and nothing else.
The only things that do not work are: 1] Output is still a PNG instead of JPEG, 2] extreme noise as well as degradation occurs as soon as post process is enabled, and the append code does nothing even with const bool CombineAtlasesOnOutput = true;. These problems occur even though the code has been edited and compiled as per instructions. The post process resulting in degradation has been mentioned as a comment in the code.
Banding and noise can be removed but it requires very high quality settings.
EDIT: This is in version 4.15.1