Is there a workaround (1) to close the inbound shipment lines and (2) to receive quantities beyond the inbound shipment quantity? Or do I need to receive the quantity in full and create an Inventory Adjustment for the quantity that should have been closed? How about the overage?

I’ve never found a way to handle an overage natively with inbound shipments… what you described is what we tried. Receive in the total and then do an adjustment up. One adjustment won’t matter, but if it happens a lot, depending on the quantities+values, it could materially screw up your average cost eventually. Or, instead of the adjustment, create a second PO/Inbound Shipment for the overage.