Of course. If you are in the mainland, you can directly ask the counter staff if they have a small amount of Hong Kong dollars to change money at the bank. If there is, you can ask him for it. Sometimes some banks don't, you can ask more. If you go to Hong Kong, you can find a convenience store, or if you need to recharge your Octopus card, the staff at the counter will help you change 1 0,000 Hong Kong dollars. In some areas, HK$ 500 and HK$ 1000 may be rejected. For example, if you take a taxi in Hong Kong, the driver can refuse 500 Hong Kong dollars, 1000 Hong Kong dollars. 500 Hong Kong dollars and 1000 Hong Kong dollars are not illegal without change.