Can a voice pitch change

Yes, the overall pitch of your voice can be changed through practice or working with a speech therapist. It takes work, but it definitely can be done.

Voice pitch in a note sung by an individual:

if I were to sing an A flat, that would be my pitch. Seeing as all melodies are not comprised of only A flats, I would argue that voice pitch could, in fact, change quite drastically, as Christina Aguilera insists upon demonstrating at every available opportunity.