pewc_filter_item_start_list.php

<?php
/**
 * Populate products field using SKUs from ACF field
 * Create an ACF field with the name child_product_skus
 * Enter the SKUs of the child products into this field as a comma-separated list
 */
function prefix_populate_products_through_ACF( $item, $group, $group_id, $post_id  ) {

	// Check ACF is active
	if( ! function_exists( 'get_field' ) ) {
		return $item;
	}

	$skus = get_field( 'child_product_skus', $post_id );

	// Bounce if this field or product doesn't apply
	if( ! $skus || empty( $item['field_type'] ) || $item['field_type'] != 'products' ) {
		return $item;
	}

	// Split the list of SKUs into an array
	$skus = explode( ',', $skus );
	$child_products = array();

	// Iterate through each SKU and find the child product ID
	foreach( $skus as $sku ) {
		// Add the child product ID
		$child_products[] = wc_get_product_id_by_sku( trim( $sku ) );
	}

	// Populate the child products for this product
	$item['child_products'] = $child_products;

	return $item;

}
add_filter( 'pewc_filter_item_start_list', 'prefix_populate_products_through_ACF', 10, 4 );

/**
 * Filter add-on groups ensuring that a specific group is included if the product has the child_product_skus ACF field
 * Edit the group ID in $global_group_id below.
 */
function prefix_filter_groups_by_ACF( $groups, $product_id ) {

	// Update this to the ID of the global group you would like to insert into products automatically
	$global_group_id = 72;

	// Check ACF is active
	if( ! function_exists( 'get_field' ) ) {
		return $groups;
	}

	$skus = get_field( 'child_product_skus', $product_id );

	// Bounce if this field is empty
	if( ! $skus ) {
		return $groups;
	}

	$global_group = pewc_get_group_fields( $global_group_id );

	$groups[$global_group_id]['items'] = $global_group;

	return $groups;

}
add_filter( 'pewc_filter_product_extra_groups', 'prefix_filter_groups_by_ACF', 10, 2 );