If you haven't agreed to take the photo with Anna, Ken's quest ends then and there as far as I'm aware.
If you are asking how to take the photo, it's on Thursday -> Hallway -> Garage -> Entrance and there should be Ken and Anna.
I haven't ever refused Ken buying groceries so I can't help you with what happens if you decline.
I don't think you can manipulate save files easily. I just restart if I've completely screwed something