How do we reconcile the verse "There is no changer of the words of Allah" with our belief in the distortion of the Gospel, and why did Uthman burn other copies of the Qur’an?

The Quranic verses indicate that Allah does not change His words, and the purpose of this is to negate the possibility of anyone nullifying or contradicting Allah's revelation, and to prohibit changing His divine commands. Ibn Ashour mentioned that the negation of change includes the non-invalidation of meanings and truths, and the non-alteration of the Sharia (definition). Ibn Uthaymeen explained this by stating that the negation is not of existence but of legal possibility, and that the distortion perpetrated by humans is a legal alteration of speech. As for Uthman's burning of the masahif (copies of the Quran), it was to unite people upon a single mushaf (definition), after other masahif contained abrogated verses whose abrogation had not reached the owners of those masahif, and to ensure the unification of recitation, and because this mushaf upon which the Companions gathered was the one confirmed in the final recitation (of the Quran to Prophet Muhammad).