I’m a little confused by what you want to do.
When you export you will need to export the ID of the relationship. This can be done using a function in WP All Export.
An export usually exports what is in the DB, not what the return format is. Unless you’ve build something special for doing the export the “return value” setting will have not effect on what is being exported.
I do not know how you can achieve an import/update under your conditions and I would contact the developers over at WPAI to see if they have any suggestions on how to do this.
