In the case of Soubi he is a blank/nameless fighter unit so anyone’s name can be written on him (Beloved) Once a name has been written it’s suppose to be that way forever but as we know, Soubi is now the fighter unit of Ritsuka/Loveless.

I don’t know how the names are chosen since I still don’t know how Ritsuka got his name Loveless. Maybe in the later volumes name clarification will happen

Thanks for stopping by and commenting :-)