I tried a professional headshot prompt on the flux playground with a tired gym selfie and it kept it as myself, same expression, sweat, skin tone and all. It was like a background swap, then I expanded it to "make a professional headshot version of this image that would be good for social media, make the person smile, have a good pose and clothing, clean non-sweaty skin, etc" and it stayed pretty similar, except it swapped the clothing and gave me an awkward smile, which may be accurate for those kinds of things if you think about it.
It isn't mentioned on https://replicate.com/flux-kontext-apps/professional-headsho..., but on https://replicate.com/black-forest-labs/flux-kontext-pro under the "Prompting Best Practices" section is says this:
> Preserve Intentionally
> Specify what should stay the same: “while keeping the same facial features”
> Use “maintain the original composition” to preserve layout
> For background changes: “Change the background to a beach while keeping the person in the exact same position”
So while the marketing seems to paint a picture that it'll preserve things automatically, and kind of understand exactly what you want changed, it doesn't seem like that's the full truth. You need to instead be very specific about what you want to preserve.