@smd Yes, it is possible to add different attributes to variants, including product_url and description, as long as those attributes are defined in the schema of your custom catalog. In your example, you added the 'link' attribute to the variants, which should work as long as the schema of your catalog includes this attribute for the 'variant' object. Similarly, you can add a 'description' attribute to the variants, but you should make sure that this attribute is defined in the schema of your custom catalog.
To ensure that your custom catalog is properly formatted, you can use an XML validator tool to check for any errors or warnings. Once your custom catalog is properly formatted and the schema includes the desired attributes for the variants, you may be able to upload it to Klaviyo if the platform supports it and use it to create personalized campaigns.