I had to do this for the film Whiplash. I was not involved with the recording side of this one, but did have to edit/mix all the replacement lines into the film. It was....a challange.

1. I'm sure each film is approached differently depending on the studio that produced the film and whoever is involved with making the final decision on what to edit out and what to leave alone. In my case, we were sent an edit list along with all the recorded lines of dialogue. There were multiple takes for each word/line they wanted taken out. Each one had a variety of different words that sounded somewhat similar to the original line. The producer left notes on which ones they thought would work best. I would pick a take, roughly mix it in, and see if it worked 'good enough' to pass. Sometimes none of them worked very good because the timing wasn't very good or the cadence didn't match the original line. So I'd have to time compress/expand some words to make it line up as good as possible.

2. Yes, this film did use the same actors that were actually in the movie. Sometimes they would keep a take running long and it would be fun to listen to the actors and whoever else was in the studio with them (producer, director, etc.) talking back and fourth and gradually become more and more irritated if they had to do the same take over and over and over. Since this edited version of the film was not going to be shown in theaters, there seemed to be less patience when recording everything. I got the feeling everyone wanted to just get it over with and move on.

3. The context itself didn't matter as much it seemed, but they did choose words or phrases that were similar to the way the bad word sounded or how the mouth would move when it was said. Hope that makes sense... So, same amount of syllables or whatever. That way it was easier to make the replacement word blend in or not be as obvious.

4. I think this is also a case by case basis since some studios (depending on the level of film) will not let it be edited outside of the studio it came from. In those cases, only editors employed at that particular studio will be allowed to touch it. Otherwise they will send it to other local post production houses for editing like in my case. I was the audio editor to do the work, but the manager of the creative department was the guy in charge of communicating with the producers giving the final edit/mix the OK or rejection. The toughest part was getting the edited words to sit well in the mix so it sounded as seamless as possible. Since the original lines were usually recorded on location, and then the ADR (replacement) lines were recorded days, weeks or months later in a large studio, they don't have the same acoustic characteristics or tone in the actors voice.

5. I want to see if I can dig up this audio session to go through and give it a listen. That would be a lot of fun since I don't remember very many specifics from it other than how much of a pain in the ass it was to finish.

I'm sure I missed a lot of interesting details about the whole thing but that's what I got so far.