I work in a Canadian bike shop, we had a customer who wanted to buy an e-bike and ship it back to Ireland becuase our legal top speed is higher.
He found it impossible to fly with the battery, the only way was by sea. I think there was an air option but it was crazy expensive. Obviously your situation is different but the whole thing seemed a complete waste of time to me for an extra 7km/h. Especially as his wife who the bike was for was happy with 25km/h being plenty fast enough.
I would either put it on a ship and wait it out or sell your battery over there and buy a new one over here.