I think we have similar case. But, in my case I used store_distro, not item_master
Just my thought:
First, you need to define which field in item_master to be filled by code for HTS/HS and Fabric content. After that, your host need to send correct code to that field in item_master by correct mapping.
When you invoice that item, you need to set up logic in your host or middleware, for item that have parameter item_master HTS/Fabric you need special invoicing process for instance.
You can use that tables and value also (item_master.xxx) as parameter in SCI.