Wa Alaykum salam wa Rahmatullahi wa barakatu, may Allah reward you for the good question. I think you are asking two questions here.
Has the Quran changed/Altered.
Is the Quran for all times.
As for number one, we know that the Quran hasn't been changed or altered as you would find many contradictions in it's verses as Allah (swt) says in the Quran:
We have, without doubt sent down the Message; and We will assuredly guard it (from corruption).
Surah al-Hijr, verse 9.
From this we can see that Allah has taken the responsibility of protecting the Quran from corruption.
As for the second and I think this is what you or your friends may mean, is the Quran for all times?
In this case yes the Quran has been sent down as a complete guidance for the whole of mankind for all times, this includes all rules and laws to govern all aspects of life comprehensively. Now one can say that the Quran changes according to time for example and ayah/verse can be appropriate for a given time and reality, this very same verse can also be interpreted to apply to another time and another reality.
Take for example the Tafseer of the Quran there a few, if you look at Ibn Kathir's tafseer (Exegesis) you will see that he has interpreted ayahs according to his time and reality, in contrast if you look at later tafseers i.e Tafseer of Imam Qurtubi you will see that this is very different from Ibn Kathir even though the interpretations are of the very same ayahs. This is valid as the Quran is for all times and realities.
Just to give an example if you look at the time of the Prophet Muhammed (saw) there were no such things as cloning, plastic surgery etc, if Muslims claim that the Quran is for all times surely the Quran must contain the answer to these questions in terms of it's legaility etc. If the Quran wasn't for all times then we would not be able to solve societies problems.
To interpret the Quran requires great knowledge and insight and is only left to competent people i.e. people knowledge etc.
I hope that answers your question and Allah knows best.
Please do clarify your question if this isn't what you meant.