That article gives horrible advice. You should never edit any core WordPress file. That’s about the worst thing you can do. Anytime you read an article that tells you to edit a core WP file, run for the hills.
Working with this part of WordPress isn’t my area of expertise, but this should work:
add_filter( 'the_editor_content', 'my_pre_edit' );
function my_pre_edit( $content ) {
global $post;
if ( !$post || $post->ID == 0 )
$content = "This is some custom content I'm adding to the post editor because I hate re-typing it.";
return $content;
}
You can drop it in your theme’s functions.php
file.
I say give it a try on a test install to make sure it’s working correctly first. I just wrote this quickly and haven’t really tested it well enough.
Note: If any other devs stop by this thread, feel free to correct me if I’m using the wrong filter.