We had a very similar situation last year when we sailed on the Carnival Glory. We had a snag come up while we were on the ship, and I was afraid we'd need to exchange some faxes with our agent. Called Guest Services and explained the situation, and they were very helpful, giving me the fax number to the ship for our agent, and telling me there would be no charge to send or receive small documents. Turns out we didn't need to use the service, but it was nice to know we could.
Granted, you're on HAL and not Carnival, but I'd bet they'd treat you similarly. My advice would be to call them before you sail and explain the situation. That way, you'll already have all the info you need to give to your agent before you sail.