@Anek Porwal You potentially could do a few things
1. For the new integration, create a Celigo flow that exports the IF, attach a suitescript that Celigo calls to manipulate the data if it can't be manipulate just in a saved search (which is tough with these package records).
2. Since you say the ShipStation integration is locked down, I assume you're using the integration app. You could turn off the integration app flow and build a custom flow where you update the IF with this different package content format.
3. What I've done in the past is create a custom shipment record and custom shipment line record in NetSuite to bring those ShopStation shipments into first. Then have another flow to update the actual IF and package contents. The reason for this is so you can know what items ended up in what package. This is tough on default NetSuite package because it doesn't allow custom fields so you end up having to put item information into just the content text field which isn't ideal.