Question: Many verses of Isaiah are quoted in the Book of Mormon, some with changes from the Old Testament Isaiah. I assume these verses were taken directly from the Plates of Laban. The question is when and who changed the wording, or was it in the translation?
Answer: While Isaiah passages quoted in the Book of Mormon use the King James Version of Isaiah, variations from the Book of Isaiah translated from the Hebrew Masoretic Text seem to be in the nature of nuancing or clarifying the English King James Version, not the Hebrew. These variations rarely if at all reflect the original Isaiah text as can be shown from the Book of Isaiah’s own internal checks and balances such as literary devices, literary patterns, literary structures, rhetorical links, and so forth. It is therefore safe to assume that these changes crept in during the translation process and aren’t original to Isaiah.
Also reference: “These things [the Old and New Testaments] go forth from the Jews in purity unto the Gentiles, according to the truth which is in God” (1 Nephi 13:25).