Is a mistake in reading some words at the end of verses considered an alteration in the Qur’an, such as reading "عذاب عظيم" (a great torment) instead of "عذاب أليم" (a painful torment) or "عذاب مهين" (a humiliating torment), or "غني حليم" (Rich, Forbearing) instead of "غني حميد" (Rich, Praiseworthy)? And is there a rule to avoid repeating that?

The one who is skilled in the Quran will be with the noble and righteous scribes (angels), and the one who recites the Quran and stutters over it, finding it difficult, will have two rewards. One must avoid mistakes in reciting the Quran that alter the text of Allah Almighty's Book, by making an effort, reciting frequently, and solidifying memorization. It is recommended to focus on memorization and solidifying it. There are books that clarify the similar verses of the Quran and word counts, but they do not suffice over memorization, beautifying its recitation (tajweed), and solidifying it.