I have tried to change the surname in my account profile, it’s easily editing, thanks.
The problem was Yahoo still remembered the old one and still displayed the old surname in all related fields. All screen captions provided in the attachment.
1. Edited profile ‘new surname’
2. Name of mailbox remained the ‘old surname’
3. Sender name showing the ‘old surname’ in receiver mailbox
4. Sender name sometimes showing ‘(null) (null)’