Overwrite CORE function for wp_lostpassword_url and message retrieve_password

I know I can do this by editing the core files but I would prefer creating a plugin that overwrites a few functions. I am new to mucking with the core functions so please bare with me. I am using a multisite setup and I want to change the URL that are used for lost passwords and in lost password emails. Right now it uses network_site_url and I want both to use site_url and point to the individual blog and not the network master. I know I have to overwrite the exiting functions but evidently I am not doing it correctly since I get an error on password resets and it cannot find the action=lostpassword. Any help on doing this is appreciated.

<?php

/**
 * Returns the Lost Password URL and sets custom essage and URL
 *
 * Returns the URL that allows the user to retrieve the lost password
 *
 * @since 2.8.0
 * @uses site_url() To generate the lost password URL
 * @uses apply_filters() calls 'lostpassword_url' hook on the lostpassword url
 *
 * @param string $redirect Path to redirect to on login.
 * @return string Lost password URL.
 */

add_filter('wp_lostpassword_url', 'fcd_wp_lostpassword_url', 1);

function fcd_wp_lostpassword_url( $redirect = '' ) {
	$args = array( 'action' => 'lostpassword' );
	if ( !empty($redirect) ) {
		$args['redirect_to'] = $redirect;
	}

	$lostpassword_url = add_query_arg( $args, site_url('wp-login.php', 'login') );
	return apply_filters( 'lostpassword_url', $lostpassword_url, $redirect );
}

add_filter('retrieve_password', 'fcd_retrieve_password', 1);

function fcd_retrieve_password() {
	global $wpdb, $current_site;

	$errors = new WP_Error();

	if ( empty( $_POST['user_login'] ) ) {
		$errors->add('empty_username', __('<strong>ERROR</strong>: Enter a username or e-mail address.'));
	} else if ( strpos( $_POST['user_login'], '@' ) ) {
		$user_data = get_user_by( 'email', trim( $_POST['user_login'] ) );
		if ( empty( $user_data ) )
			$errors->add('invalid_email', __('<strong>ERROR</strong>: There is no user registered with that email address.'));
	} else {
		$login = trim($_POST['user_login']);
		$user_data = get_user_by('login', $login);
	}

	do_action('lostpassword_post');

	if ( $errors->get_error_code() )
		return $errors;

	if ( !$user_data ) {
		$errors->add('invalidcombo', __('<strong>ERROR</strong>: Invalid username or e-mail.'));
		return $errors;
	}

	// redefining user_login ensures we return the right case in the email
	$user_login = $user_data->user_login;
	$user_email = $user_data->user_email;

	do_action('retreive_password', $user_login);  // Misspelled and deprecated
	do_action('retrieve_password', $user_login);

	$allow = apply_filters('allow_password_reset', true, $user_data->ID);

	if ( ! $allow )
		return new WP_Error('no_password_reset', __('Password reset is not allowed for this user'));
	else if ( is_wp_error($allow) )
		return $allow;

	$key = $wpdb->get_var($wpdb->prepare("SELECT user_activation_key FROM $wpdb->users WHERE user_login = %s", $user_login));
	if ( empty($key) ) {
		// Generate something random for a key...
		$key = wp_generate_password(20, false);
		do_action('retrieve_password_key', $user_login, $key);
		// Now insert the new md5 key into the db
		$wpdb->update($wpdb->users, array('user_activation_key' => $key), array('user_login' => $user_login));
	}
	$message = __('Someone requested that the password be reset for the following account:') . "\r\n\r\n";
	$message .= site_url( '/' ) . "\r\n\r\n";
	$message .= sprintf(__('Username: %s'), $user_login) . "\r\n\r\n";
	$message .= __('If this was a mistake, just ignore this email and nothing will happen.') . "\r\n\r\n";
	$message .= __('To reset your password, visit the following address:') . "\r\n\r\n";
	$message .= '<' . site_url("wp-login.php?action=rp&key=$key&login=" . rawurlencode($user_login), 'login') . ">\r\n";

	if ( is_multisite() )
		$blogname = $GLOBALS['current_site']->site_name;
	else
		// The blogname option is escaped with esc_html on the way into the database in sanitize_option
		// we want to reverse this for the plain text arena of emails.
		$blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);

	$title = sprintf( __('[%s] Password Reset'), $blogname );

	$title = apply_filters('retrieve_password_title', $title);
	$message = apply_filters('retrieve_password_message', $message, $key);

	if ( $message && !wp_mail($user_email, $title, $message) )
		wp_die( __('The e-mail could not be sent.') . "<br />\n" . __('Possible reason: your host may have disabled the mail() function...') );

	return true;
}

?>