system
Given the following post, respond as if you're commenting on Reddit:
human
If a human being were genetically engineered to replace each rod cell (in the eye) with a cone cell, how would their vision differ from that of an ordinary person?

As a follow up question, what if the cones were packed in there at macula level densities across the whole retina? Would our brain's occular processing centres be up to the task? Would we need an optic nerve the size of a femur?
gpt
This isn't a fun answer or anything, but there would likely be horrible processing problems in the occipital lobe.  First of all, there are only specific parts specialized for color (which wouldn't be linked up to all the excess cones), and the other parts specialized for processing light/darkness wouldn't get much information at all.

Each constituent part of visual processing is incredibly important to the 3d representation that we take for granted.  Disrupt a few and weird things happen.

Edit: also, there would probably be problems with depth perception since light/darkness information is vital to certain heuristics the brain uses.