After pushing back, you are called on the Ops Frequency and informed "Your Zero Fuel Weight has changed. Ten late bags were added in the aft bin." Shortly after that information, you receive an ACARS message from Dispatch informing you of the same change to the Zero Fuel Weight. Can you make the adjustments in the OPC and FMC and takeoff in a -700, or do you return to the gate for an amended Loading Schedule? How about in an -800?