You need to make a distinction between belief and practice.
Islam is a religion of the book, and two books are involved; these books are the Qur'an and Hadith. What the prophet taught, and what the companions of the Prophet told about the prophet are cast in Arabic forever, never to be altered.
How people practice that in their personal lives is what has changed. This does not refer to the five pillars of Islam nor to the Salat or prayer. It refers to how Muslims live with peace and compassion for all mankind, of whom they are one with.
- There is only one race, the human race.
- There is only one language, the language of the heart
- There is only one religion, the religion of love
- There is only One God, and he is omnipresent.