It have nothing to do with feedback but ratings. When ratings are not good, writers change the script to spice it up. Most of the dramas change quite a lot as they go. This is why writers work full time with assistants until the end of the show.
Especially the ones that have over 100 episodes :D I think at the start of filming, everyone knows how to start, have a raw image how to progress and ending. Everything else gets filled in progress.
Also got a new advertisement offer? Have to cut part of the script, insert AD and adapt it to the story.
Dramas with better funds and good actors usually avoid that but cheaper ones, most of the time try to adapt to ratings.
I have read several interviews with writers. They told how stressful their job is since sometimes they have to change the story completely during filming. That can happen even to well funded drama.
Perfect story and cast but ratings are just not there. No options but to change things. It's not like you can cancel the show when it starts airing.
...aaaand here comes the horror of pre-produced drama. Let's say ratings are low. Can you change something or adapt? Nope. The best example is 'Entourage'. I liked it since Kwangsoo was in it but Koreans didn't like american vibe, ratings were 1.0%, a commercial failure. They would have changed plot or characters for sure if it was filmed while airing.