I am using ShipCompliant with Nexternal. I have the autosynch turned on (in Settings / Compatible Software). I have just modified an order to change the customer's address and add an item to the order. Do I need to re-synch this order, or will the autosynch take care of it?
You need to manually re-synch the order. There is a simple button on the bottom of the order where you can do so. The autosynch does not search for changes in orders, but rather looks for status changes such as checking Nexternal for orders that are paid and ready to ship (depending on your settings), or canceled and need to be canceled in ShipCompliant, or looking in ShipCompliant for orders that are shipped and have tracking numbers that need to be pushed into Nexternal.