For a long time I didn't have any reason to add two different Google accounts to the same phone, but obviously you can. You can have one Google account that's for the U.S. and one that's for HK, and within the Google Play store you can easily and quickly switch between the two Google accounts.

This isn't for the HSBC Reward+ app, but Xiaomi also has the feature called dual apps, which I used to create a Hong Kong version of the Mi Home app and a mainland China version of the Mi Home app on my phone. I couldn't use my Hong Kong bought Mi air purifier alongside my gray import mainland China Mi products within the same Mi Home app, so a dual app solved that problem.

In summary, you can use multiple Google accounts and other kinds of accounts to deal with country-specific digital restrictions.

Additionally, you can also use a VPN to digitally be in almost any country you want to in order to use whatever country-specific website and/or digital service you want. For a free VPN to the U.S. I use Hotspot Shield, and at least a few websites will block you if you are using a non-U.S. IP address to access their site.