That stupid "lucky to get out of there" line wasn't a new change for the SEs; it was in the original script.
The dialogue "You're lucky you didn't taste too good", was not redubbed. There were several variants of this line in the shooting script. All of the special editions used different takes every once in a while; mostly because some were of much greater quality than the others. The particular take that Lucas approved for this scene had Hamill reading straight from the script, instead of ad-libbing the now famous comment. Lucasfilm officials have stated that they didn't realize the dialogue was any different until the film was released. This also accounts for some of the other minor dialogue changes in the SEs.
Hmm, interesting. I remember from Irvin Kershner's commentary on my ESB dvd that he added in a bunch of stuff like that, by encouraging ad libbing in scenes where he felt more was needed. Probably most famously was the "I love you. I know." exchange between Han and Leia, originally written for Han to reply "I love you too." After a bunch of takes, Harrison Ford finally came up with the "I know" line, which to me is one of the best moments in the trilogy--the line is so good you almost couldn't write it. Kirshner also added little moments to R2 and Chewbacca, infusing them with warmth and personality. Definitely recommend checking out his commentary to anyone who hasn't. I have the '08 boxset with the original theatrical versions on it, so as long as I've got that, I'm fine.