If you want to use the same product modification item in several stores, you won't need to create a new one each and every time. Simply copy it and select the store you want to add it to. Here's how you do that.
1. Navigate to the Catalog on the left sidebar.
2. Expand the Product Modification Items menu and select the store where your item is located.
3. Find the product you want to change and click the copying icon.
4. Using the dropdown menu choose the store where you want to add this product and click Save. You'll see the list of product modification items of this store.