They are. Edits in comic books could range from color adjustments to reworking dialogues or adding/removing panels to better suit the overall theme and flow.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.
Well, for copy editing a novel, you need to focus on language accuracy. That means correcting punctuation, fixing word usage, and ensuring the sentences are structured properly. Another important aspect is to maintain the author's voice while improving the clarity and flow of the text.