Stock Sync supports multiple values in one column for update and import feed which allows the users to update or import the variants that have multiple values in one column.
To enable this option, please reach out to support@stock-sync.com
For example, if the feed file has the variants S,M,L,XS,XXL and you want to use them to update it. You can enable this option via the support team. It only supports the options fields and quantity fields. Refer to the image below as an example: