When admin changes a password for a registered user, I don’t want to send a password change email to users

See 'send_password_change_email' filter hook.
It is part of the wp_update_user() function, fired on admin or on frontend… So I think you can check if the update is done via the admin, then if true, deactivate the email this way…

if ( is_admin() )
    add_filter( 'send_password_change_email', '__return_false' );