Change WordPress’ Default “Register For This Site” Message To Your Own Custom Text

change_reg_message.php

function change_reg_message($message)
{
    // change messages that contain 'Register'
    if (strpos($message, 'Register') !== FALSE) {
        $newMessage = "Hello! We're so excited to have you as a member! Just enter a username and your email, and we'll have you squared away in no time.";
        return '<p class="message register">' . $newMessage . '</p>';
    }
    else {
        return $message;
    }
}

// add our new function to the login_message hook
add_action('login_message', 'change_reg_message');