How to have certain WordPress settings set by default on a per author basis

To check if s/he is the right author, you can use is_author() function using the author id or name as parameter. And, depending on how you set up the settings for displaying author box or last updated. You can put your settings.

I am considering your settings are in options table. So I will use `

if( is_user_logged_in() && is_author('4') ){
  update_option( 'display_author_box', true );
}

If you want to show him customized posts, you can do that with a query.

Hope this helps.

References:
is_author() function
update_option() function

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