External Images already supports multiple image paths. It’s recommended to use the pipe separator since some image URLs from some CDNs actually contain commas, otherwise you can also use commas.

Multiple images works for image galleries, but you can also have multiple images for image variations meaning you can have variation galleries too.

To add multiple images, you have two choices – you can import pipe (or comma) separated image URLs to the external_image_url custom meta field, or you can keep that field just for your featured images and import your image galleries (pipe or comma separated) into the custom meta field called ‘gallery_urls’.

https://www.superspeedyplugins.com/knowledgebase/how-to-alter-import-jobs-to-import-external-images/