In this comment, there is a reference to "some of the lines that Harrison Ford/Sir Alec Guiness allegedly refused to say". Poking around (admittedly briefly) online, I couldn't find any references to these lines. Are there examples somewhere?
Ford refused to say, "I love you too".
Here's one example. When filming The Empire Strikes Back, Harrison Ford refused to say "I love you, too", which was the scripted response to Leia's "I love you".
On the day he shot the carbonite scene in June 1979, director Irvin Kershner was actively making changes to screenwriter Lawrence Kasdan’s script. Amazingly, there’s a complete record of when and how these changes occurred, because unit publicist Alan Arnold was recording everything on audio cassette. In a conversation between Ford and Kershner transcribed in Rinzler’s book, the director and star agree that the love scene needs to be less florid.
“I think she ought to just say, ‘I love you,’ as I’m passing by her,” Ford suggests to Kershner. Later in the conversation, he makes the change to his own line, saying, “If she says, ‘I love you,’ and I say, ‘I know,’ it’s beautiful and it’s acceptable and it’s funny.”
...When Kershner put his first cut of The Empire Strikes Back together, executive producer George Lucas pushed back against the new dialogue, fearing that the audience would laugh at Han’s line...“When the film was over, people came up and said that is the most wonderful line and it worked. So George decided not to have the second screening.”