You cited a narration from Sahih Bukhari in order to support your claim that the Qur'an has been changed,
Let me distance myself from that claim. I do not and would not claim that the Quran had been changed. That would be foolish because it would lead to a ban and I do not know enough to make that claim anyway. Presumably I made some other claim but I cannot remember what it was. I will get back to you once I have checked.
but there are a couple of points to note:
-if that verse was not in the Qur'an at the time of Umar and was supposed to be, then why wouldn't he and the other companions include it in the compilation? Why would they not include it and then warn people that a time would come when people would think the ruling of rajam was not revealed?
I do not know. But why would Bukhari have included that hadith in his collection if he knew it was wrong? It is not the changing that I would argue about, but the degree of open-mindedness. Whatever was or was not done to the Quran (and I would prefer to leave that topic well alone) Bukhari was willing to consider that perhaps a verse was left out. No one around here is any more I bet. That change is interesting to me. The Quran is less so.
-if you think Umar was warning the people of a time in the future when that verse may not be part of the compilation, then how did Umar know that the verse would later be removed?
It is not important, but is that what he is saying? I think he is saying that it was not in the Quran when he was speaking, and he was worried that people in the future would argue that because it is not in the Quran they would no longer stone. So it had been, well not removed, but not found in the Quran when he was speaking. What he was saying was that it was not in the Quran when he became Caliph, and so he needed to assert that Muhammed had stoned and he would too.
Sahih Bukhari Volume 8, Book 82, Number 816:
Narrated Ibn 'Abbas:
'Umar said, "I am afraid that after a long time has passed, people may say, "We do not find the Verses of the Rajam (stoning to death) in the Holy Book," and consequently they may go astray by leaving an obligation that Allah has revealed. Lo! I confirm that the penalty of Rajam be inflicted on him who commits illegal sexual intercourse, if he is already married and the crime is proved by witnesses or pregnancy or confession." Sufyan added, "I have memorized this narration in this way." 'Umar added, "Surely Allah's Apostle carried out the penalty of Rajam, and so did we after him."
The above two points are sufficient to refute your interpretation of the hadith. As for the correct interpretation, this is one of the verses whose recitation has been abrogated, yet its ruling remains. It has nothing to do with alteration of the Qur'an.
Which interpretation is that and how does it refute anything? I do not follow your interpretation - you are claiming that the verse on stoning was revealed, but it is not important for Muslims to recite it and so it was not included in the Quran but the ruling remains in effect? This just raises more questions than it answers - how many other revelations are not in the Quran in your opinion?
I will look up exactly what I said and perhaps we can try again to discuss that?