We use the sp-api for various tasks without any problems. We don’t have PII access.
One of the things I do is pull down an item list report (GET_MERCHANT_LISTINGS_DATA), but unfortunately that report doesn’t have a column indicating whether an item is customized. I also checked the Catalog Items api, but similarly I don’t see any indicator for whether an item has customization set up.
I dug around in various docs etc and of coursed searched online, but no luck. I do see a lot of people are trying to pull customization for orders - but in my case I’m just trying to pull my whole item list and get indication of which items are customized and which aren’t.
Doesn’t help for the current but in the future it might be as simple as making the SKU with a “C” at the beginning or ending of the SKU. You would be able to see at a glance in most reports in excel (and be able to filter and/or sort).