using TREK rules and cannon, far as the characters are concerned there prime universe has been changed.
Not this time, it hasn't.
Not only have the writers themselves said so, but Spock Prime's presence is proof enough.
How does Spock Prime being there prove that?
Why because hes there after history is changed ? Picard and co were there in FC after The Borg changed Earth's past and that wasn't different timeline. ST inidcates if you go back in time your protected from the timeline changes...You become seperate from the universe not the other way around.
The writers are threw a bone to some fans because they were ready to lynch the writers for changing the timeline despite always hating RESET buttons in time travel stories