If you’re adding extra fields to variable products, you can choose to create different fields for different variations.
When you add a new field, you’ll see the ‘Variations’ section at the bottom of the field parameters.
If you only want to show this extra field for certain variations, just type the variation ID(s) into the field.
Now, the extra field will only appear when the variation is selected.
Please note that variation specific fields are only available on add-ons applied to individual products, not for global add-ons. Also, the ‘Variations’ field will only appear after your product has been saved or published. It’s not visible on new products.