It's of course technically possible but it's also much more difficult. You basically have to photoshop a long series of frames and make sure that it looks natural and consistent in sequence. You have to take into account changes in lighting, focus, motion blur, things passing in front and behind the object etc...

In your example they modified a very clean source video, image is perfectly stable, very little motion and they edited a very small portion of it for a very short duration. TFA is about replacing one person by an other while they're talking and moving on a potentially lengthy video clip. Doing this convincingly by hand would be hard work.

I think a good example of the difficulty is with the infamous "moustache removal" for reshoots of Superman in the Justice League. It cost a fortune and the results were not exactly seamless. Also the re-created Princess Leia in that Star Wars movie, not bad but definitely still in the uncanny valley.