The words of the Lord are perfect in truth and justice;there is NONE who can change His words.He both heareth and knoweth.-- Sura 6:115
None can change the words of God;-- Sura 6:34
There is no changing the words of God;that is the mighty triumph.-- Sura 10:64
And recite what has been revealed to you of the Book of your Lord,there is none who can alter His words;and you shall not find any refuge besides Him.-- Sura 18:27
And for whatever verse we abrogate and cast into oblivionWe bring a better or the like of it;knowest thou not that God is powerful over everything?-- Sura 2:106
And when We exchange a verse in place of another verse --and God knows very well what He is sending down --they say, 'Thou art a mere forger!'Nay, but the most of them have no knowledge.-- Sura 16:101
Here is Ibn Kathir's commentary on Sura 18:27 taken from Tafsir Ibn Kathir, Abridged Volume 6 (Surat Al-Isra’, verse 39 To the end of Surat Al-Mu’minun), abridged by a group of scholars under the supervision of Shaykh Safiur-Rahman Al-Mubarakpuri, Darussalam Publishers & Distributors, Riyadh, Houston, New York, Lahore; First Edition, July 2000:
The Command to recite the Qur’an and to patiently keep Company with the Believers
Commanding his Messenger to recite his Holy Book and convey it to mankind, Allah says,
Muhammad Asad comments on the same verse:
"... According to Razi, it is on this passage, among others, that the great Qur’an-commentator Abu Muslim al-Isfahani based his rejection of the so-called ‘doctrine of abrogation’ discussed in my note 87 on 2:106." (Asad, Message of the Qur’an [Dar Al-Andalus Limited 3 Library Ramp, Gibraltar rpt. 1993], p. 443, fn. 35)
The following Muslim cites Sura 10:64 as proof that the Quran is unchangeable:
5. Why don't Muslims adapt the Quran to the needs of the modern age?
a.The Quran states: there is no changing the words of God. (1) (Source)
In the footnote, this is what we find the author citing:
1Those who believe and guarded (against evil): They shall have good news in this world's life and in the hereafter; there is no changing the words of Allah; that is the mighty achievement.Sura Yunus (10) verses 63/64 (Source)
The problem is obvious: On the one hand, Sura 6:115, 6:34, 10:64, 18:27 make it clear that NONE CAN change the words of God (which is supported by the explanation of the commentators quoted). But, on the other hand, God DOES exchange one verse for another verse (Sura 2:106, 16:101). And he does so through his messengers like Jesus [supposedly changing some rules given through Moses] and like Muhammad who gives rules different again from those of Moses and of Jesus.
Answer: Simple: change of God words or change to a new message is only done by God. So no one change God's words and messages except him. Though Quran and Islam is for all the world and it is the duty of all Muslims to spread Islam without oppressing or discriminating anyone. It appears that the world will be one religion only when Christ comes to earth. But we can make a better world ready for him.