Anyone with a valid passport can ask for a visa.
No, you can't do that. To do this, you will need to leave the country and apply for a new one.
No, the one country, two systems policy is used by both countries. So, you will have to get a visa for this territory. Now that you know all about the different kinds of Hong Kong visas, it should be easier for you to get one. Before going to a country, you should know a lot about the different visa types offered by the country. This will make your trip go more smoothly.
After you send all of your documents to the Hong Kong Immigration Department, it can take up to 4 to 6 weeks for your visa to arrive. Depending on what the Immigration Department finds out, it may take longer than that sometimes.