Are the earliest scriptures of the Quraan that have been found the exact same as the current version of the Qur’an? What are done evidences of that? I have heard that there are claims saying that there have been changes in the vowels and letters (small changes) but contribute largely to the difference in meaning.

How and why did the pronounciation get modified?

1) Yes, there was a difference in the form of recitation and sounding, but the scripture, content and meaning are the same

2) This is just a normal process of change in the use of language and pronunciation. All languages undergo change in how they are spoken over many years