I did not fully understand this exercise. I have made two different versions of the same photograph, one where I have selected the face and increased the contrast and brightness of the face and the second where I have adjusted the hue and saturation of the eyes. I prefer the first although I think that could be just this particular example.
On both photos I have kept the adjustments light, just enough to enhance the face or eyes but nothing too obvious. To me the second adjustment where your changing the eyes is the more ethically difficult. Changing the saturation wasnt so bad but once I changed the hue the model has different colour eyes.
I am sure that this type of adjustment has its place though. Intention would play a big role on deciding where to draw the line, I think. I would find it hard to deliberately change a portrait of somebody in order to deceive. If my intention was to make something obviously fake, that people would see it as this, then that would be different.