You don’t need to switch account in order to update the app. You only need to input the password to update. Also, don’t change App Store region, or some of your purchased items, such as movies, may be gone forever.
Further, the logged in iCloud Apple ID can be different from the App Store logged ID. It means that you can login your hk Apple ID to sync your iCloud date while login UK App Store to purchase UK app with your UK Apple ID.