As Nephi continues to quote Isaiah (chapter 13), he actually manages to make a few changes of greater importance than simple punctuation.
In verse 3, he alters a few words to clarify that God's "mighty ones" and those that "rejoice in [his] highness" are exempt from his anger. I suppose that's a fair thing to point out, as the King James version of this verse does make it sound a little weird, but it's hardly earth-shattering revelation.
In verse 8, Nephi removes the phrase "they shall be in pain as a woman that travaileth," which simply amounts to extracting a bit of imagery.
In verse 15, Nephi adds a little specificity. He amends Isaiah's comment about people being "thrust through" and "falling by the sword" to point out that these people will be those who are "proud" or "joined to the wicked." Helpful, I suppose, but nothing to build a testimony on.
And in verse 22, Nephi adds a closing statement to the chapter: "For I will destroy [Babylon] speedily; yea, for I will be merciful unto my people, but the wicked shall perish." The destruction of Babylon has been prophesied roughly a bajillion times, and God's proclamations of destroying the wicked and preserving "his people" are just as plentiful throughout the scriptures.
For a book that is claimed to have the "fullness of the gospel" and the preserved "plain and precious truths" that have been removed from the Bible, the Book of Mormon's quotations from the Bible are pretty sparse on the precious doctrines. There are some differences between Isaiah and Second Nephi, but I've seen nothing so far that is important enough to merit including a dozen chapters of Isaiah (in their entirety).
I think I only have two Isaiah-quoting chapters left. Are we there yet?