Well, M2E Pro solution works by taking information that you choose for your listing from Magento Catalog and sending it to the marketplaces. Changing any information in your Magento is not a purpose here. That's why you can’t find information about your question.
I suppose feeding Magento with the ready ASINs is something your developers could do. After your products are assigned with ASINs, you can take that information from the database and put it in Magento attribute. That way, it would be something similar to the process that you want.