gistfile1.txt

remove_action( 'woocommerce_proceed_to_checkout', 'woocommerce_button_proceed_to_checkout', 20 );
add_action( 'woocommerce_proceed_to_checkout', 'change_url_to_checkout', 20 );
function change_url_to_checkout() {
	$cart = WC()->cart->get_cart();

	$url = '';
	foreach ( $cart as $item ) {
		if ( $item['product_id'] === 70 ) {
			$url = 'put_your_extra_page_url_here';
			break;
		}
	}

	if ( empty( $url ) ) {
		return;
	}
	?>
		<a href="<?php echo esc_url( $url ); ?>" class="checkout-button button alt wc-forward">Your checkout</a>
	<?php
}