Hi, @quiztrail! Thanks for starting this thread. Which theme are you using?
At the moment, I’m afraid there isn’t a built-in way to customize product recommendations on any of the free Shopify made themes. This is because Shopify has developed its own algorithms for product recommendations. The system pulls data on products that were purchased together, as well as products with similar descriptions, to provide a mix of these as recommendations for the product currently being viewed.
When there is no data regarding co-purchases or similar products, a collection-based product recommendation option will be shown. This fallback goes to the collection from which the URL was generated, and pulls other products from that same collection. If the product did not come from a collection URL, the system will find collections the product is in, and pull other products from those - ‘All’ and ‘Featured’ collections would be excluded from these though.
That being said, customizing the recommendations would require advanced development skills in order to include or exclude certain products from showing. Therefore, if this is a customization you’d like to move forward with, please reach out to a Shopify Expert via the Experts Marketplace to discuss it further.
Hope this helps!