Please create “Tag SKU” and “No Price” attributes first.
Then create a note SKU and check on the “No Price” checkbox (new attribute).
Finally, add the note SKU in the “Tag SKU” text box (the new attribute) of the SKUs which need the notes. If you have multiple note SKUs, use ; or , as delimiter for Tag SKUs. eg: SKU1,SKU2
https://support.woopos.com/knowledge-base/creating-a-tag-sku/ (Method 1)