Posting the SKU more than once to WooCommerce

Important: This is a non-standard WooCommerce ability that affects product SKUs, and might interfere with 3rd party WooCommerce plugins. Please check the installed plugins before enabling this option. 

Go to WooCommerce settings -> Account settings -> Variations

Set the "Allow sending same product twice" setting

• if unchecked, the product is sent to WooCommerce with main variation SKU (Standard). Trying to post the same product twice, will result in the error "This SKU is already on WooCommerce, cannot be posted twice".
• if checked, products will be sent to WooCommerce with the generated sku (Extended) in format sku@parent_id. This creates unique SKU for each variation and allows cross-posting of products as variation of each other. 

Explanation

Standard WooCommerce operation requires that the product SKU will appear in the inventory only once. Therefore, for 2 example products "White Gold Ring" SKU 123456 and "Yellow Gold Ring" SKU 654321, it is not allowed in WooCommerce to create 2 products with variations referring to each other, as follows:

• WooCommerce Product1
  • Main product: "White Gold Ring" SKU 123456
  • Variation: "Yellow Gold Ring" SKU 654321
• WooCommerce Product2
  • Main product: "Yellow Gold Ring" SKU 654321
  • Variation: "White Gold Ring" SKU 123456

To overcome this, with the enabled "Send same product twice" option, Valigara posts the following products.

• WooCommerce Product1
  • Main product: "White Gold Ring" SKU 123456@123456
  • Variation: "Yellow Gold Ring" SKU 654321@123456 
• WooCommerce Product2
  • Main product: "Yellow Gold Ring" SKU 654321@654321
  • Variation: "White Gold Ring" SKU 123456@654321