As of API version 2023-07, you can now subscribe to the orders/updated webhook to be notified of any sale attribution edits to an order. When a staff attribution edit is made on POS, the orders/updated webhook will fire. The payload will include a new attributed_staffs field under line_items. This new field will reflect the new attributions on the order after the edit.
A user can edit the staff attributions on multiple line items at once on POS. In this case, the webhook payload could include multiple updated line items with different attributions applied to them.
Note that the payload in the orders/create webhook will also be updated to include attributed_staffs.
Learn more about webhook on Shopify.dev.