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I don't think I could change a book from 3rd to 1st person just by searching and replacing. If only because I write very differently in 1st person than I do in 3rd person. 3rd person, I have the narrator talking, whether visible or invisible to the reader, and the narrator has a tone of voice that is how the story is told. In 1st person, the tone of voice comes directly from the character who is speaking, and thus sounds like him. It changes everything for me.
I've always thought that was how a good 1st person novel works. I've seen some (and own some) 1st person novels that feel like 3rd person, just with the word "I" instead of "he" tacked in, and I always though they came off as stiff.
Maybe it's just me.
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