If someone, previously named John Smith, now changed to Mohammed bin Usman, is there a word to describe such a person?
I don't think there is an actual noun for such a thing. The only way I can think of to describe these people is to use a verbal phrase:
Would all of the people who have been renamed please move to the other side of the room.
From Merriam-Webster's definition of rename:
: to give (someone or something) a new name
// renamed the street in honor of the late mayor
// . . . a 16-year-old who left the Orthodox life a year ago. He has renamed himself Adam to cement the break . . .
— Ron Kampeas
// The program was actually a relatively simple . . . script that renames files on your hard drive . . .
— Michael J. Miller
You could coin a new term such as new-names, and it might even be understood, but it would certainly not be in common (or even uncommon) use.