You are able to update products Matterhorn with Stock Sync. Just choose on Matterhorn template after choosing to update existing products in your store. 

1. Go to Setup New Feed > Choose Update existing products.

2. Choose or search for Matterhorn template.

3. You can select the currency needed for the Matterhorn products in the first step. There are two options which are EUR and USD

4. Click Next to the field mapping section.

These are the available fields that can be added with Stock Sync.