A scholar has cited the underlined portion of the following verse to convey that no verse of the Qur’ān has been abrogated.
And recite what has been revealed to you [O Muhammad] of the Book [the Qur’ān] of your Lord. None can change His Words, and none will you find as a refuge other than Him. (18:27)
Whether any verse in the Qur’ān is abrogated or not is something that can be debated; however, this much is certain that the above quoted verse does not support the view of abrogation.
You see the Qur’ān is a coherent book and each verse should be understood with reference to its context. 18:27 is actually connected to 18:6-8. The in-between verses are parenthetical in nature and are just an answer to a question regarding the Ashābu’l Kahaf (people of the cave) raised by the People of the Book to tease the Prophet (sws). The word ‘Kalimah’ refers to the established practice of the Almighty regarding His law of guidance. 18:6-8 reads:
Perhaps [O Muhammad!] you would fret yourself to death, following after them, in grief, if they believe not in this Message. That which is on earth We have made but as a glittering show for the earth in order that We may test them – as to which of them are best in conduct. Verily what is on earth We shall make but as dust and dry soil. (18:6-8)
These verses ask the Prophet (sws) not to fret over the disbelievers if they are not accepting faith. Now 18:27-8, while referring to the law of the Almighty regarding guidance, say that this law is unchangeable and the Prophet (sws) need not fret over these rich and arrogant people. It is not that he is lacking in effort that they are not accepting faith. In fact, it is their love for this life that stopping them. The law of the Almighty is that people who do not want guidance are not given guidance. So he must not fret over them. This law of the Almighty is unalterable.
In other words, the underlined portion of 18:27 given above refers to this unchangeable law of guidance and does not mean that the verses of the Qur’ān cannot change.