PrestaShop eBay Integration manual
Custom Item Specifics
You can also create your own product item specifics. For doing this please fill “Custom Item Specific” inside Selling Profile and Category Mapping.
To add new specific you need to provide a name and it's value. If one name already exists in normal pre-defined specifics, data will be rewritten with custom.
The module allows you to specify any custom variable inside value, the same way as you can do inside the Description template (please see PrestaBay Variables for more details).