Is Google's Product field 'This is a custom product' available in the Shopify API?

[Parasoul]

Shopify's official Google Shopping app stores the data in Product Metafields and they can be accessed with the namespace 'google' where you have various keys available like

'MPN'

'google_product_category'

'google_product_type'
'title_tag'
description_tag'

'condition'

etc.

However, one field that seems to be missing is the 'This is a custom product' that is available from the Shopify Admin / Google fields editor. Does anyone know if it is possible to read/write that field from the GraphQL (or rest) API and how?