Customize Pre-Order Products

functions.php

<?php
add_filter( 'body_class', 'add_preorder_class' );
add_filter( 'post_class', 'add_preorder_class' );
function add_preorder_class( $classes ) {
	global $post;

	$product = wc_get_product( $post->ID );
	if ( $product && 'yes' === get_post_meta( $product->get_id(), '_wc_pre_orders_enabled', true ) ) {
		$classes[] = 'pre-order';
	}

	return $classes;
}

add_action( 'woocommerce_before_shop_loop_item_title', 'show_preorder_badge' );
add_action( 'woocommerce_before_single_product_summary', 'show_preorder_badge' );
function show_preorder_badge() {
	global $post, $product;

	?>
	<?php if ( 'yes' === get_post_meta( $product->get_id(), '_wc_pre_orders_enabled', true ) ) : ?>

		<?php echo '<span class="onsale pre-order">' . esc_html__( 'Pre-Order!', 'domain' ) . '</span>'; ?>

	<?php endif;
}