At this time it does not appear that this is possible to manage via OCAPI.
I suspect that in the future you'd be able to achieve it using the following resources:
DELETE /catalogs/{catalog_id}/categories/{category_id}/products/{product_id}
followed by:
PUT /catalogs/{catalog_id}/categories/{category_id}/products/{product_id}
With a ProductCategoryAssignment
document in the PUT
call.
However, this would require that Salesforce adds those attributes to the ProductCategoryAssignment
document.
The reason I suggest this is where it would be added is that within a catalog import document (XML) the flags are associated with a similar resource representation. eg:
<category-assignment category-id="gear-bags-backpacks" product-id="NSF4003100">
<primary-flag>true</primary-flag>
</category-assignment>