Via the API
We've added the param 'upc_does_not_apply'. Setting to true will apply the setting.
Via Shopify
A new custom tag called 'reverbsync-upc-does-not-apply:on' can be added to your Shopify Products.
Via Bigcommerce
A new custom field called 'reverb_upc_does_not_apply' should be set to value 'on'.