Function to change a label (Username) in a core WordPress File (wp-includes/general-template.php)

Question

Would like to change

'label_username' => __( 'Username' ) on line 258 of wp-includes/general-template.php to 'label_username' => __( 'Username or Email' )

Changing core files is a not recommended --- never never

So any help to code a function to achieve this would really be appreciated.

Answer 1

Try putting this in your functions.php

function wpse60605_change_username_label( $defaults ){
    $defaults['label_username'] = __( 'Username or Email' );
    return $defaults;
}
add_filter( 'login_form_defaults', 'wpse60605_change_username_label' );

Answer 2

You should hook to the gettext filter which is called by __() function on domain translated text with the untranslated text as second parameter.

Take a look at how to use gettext filter for changing the comment form.