We've got custom properties being added to product details from the product and order details page (i.e. a custom option like monogramming specified the customer is correctly being included in an order). The line items show on the order details page but do not show in the order export. Can this be changed? If so, how? A Shopify Guru suggested using the order API but I feel like that's superfluous.
To my knowledge, you cannot modify the output of order exports. Take that with a grain of salt though, maybe, because it's not a concern of the API, so it's a little bit out of my area of expertise.
In what way do you feel the orders API is superfluous? You could write a script which essentially consumes all orders on a shop with their line item properties, the only major difference is that you won't be given a single CSV, but a collection of JSON objects in memory which you can do whatever you please with (including serializing it all to a CSV yourself).
Let me know what you think.