Replace the description tab with a custom function in WooCommerce

add_filter( 'woocommerce_product_tabs', 'woo_custom_description_tab', 98 );
function woo_custom_description_tab( $tabs ) {

	$tabs['description']['callback'] = 'woo_custom_description_tab_content';	// Custom description callback

	return $tabs;
}

function woo_custom_description_tab_content() {
	echo '
Custom Description
';
	echo '
Here's a custom description
';
}