Very easy. If you 填表去入境處話會放棄, you can simply wait until the visa is issued and agree with your agent the arrival date of the new maid. Pls note that it will usually take 1.5-2 wks after the visa issued. If you don't want the new one meets the old one, you can terminate her on the day before the expected arrival and ask her to leave immediately. However, my friend has a bad experience. She terminated the maid in the morning of the expected arrival date but the agent contacted her in the afternoon that the maid no show at the airport due to a sudden serious sickness.