Sometimes WP's setup is utterly confounding.
Almost everything is in some way customizable via css, template files or functions.php, but trying to customize the structure and layout of the "Reply" form (that follows a blog post) is buried in the deepest parts of wp-settings and wp-config files. I have no idea why this is different.
In the "comment-template.php" include file (in wp-includes) the commented section says that you can add variables to the $defaults array...but is this change permanent or will it just be overwritten during the next WP update?
Does anybody know?