ios-appstoreiphoneitunes-store
I have recently changed the App Store region to South Korea, as I'm currently living here. I'd like to know if there is any way to change the currency of the App store without changing the country of the store?
I think it cannot be done but my husband insists that I have to change it because Apple charges more in KRW than USD.
I am using an iPhone 7.
Per my comment above, apps simply do not show up (in iTunes itself, anyone can view the web-page overview versions) in iTunes if they are not available in your region.
If you do follow a link to the app specifically, you should get an error message explicitly stating that the application is not available. Any other message indicates some other problem entirely.
Your mother's iPad will take you through the process of creating an Apple ID, but you can also create one on her behalf at Apple's website. Whatever you specify as the country of her mailing address there will determine the Apple Store she becomes associated with.
So the answer to your first question is yes, it is based on the Country/Region you specify when creating a new Apple ID.
The answer to your second question is no, it doesn't matter what you set as the regional localization of your iPad itself. You can change the iPad's localization as often as you like, indeed I do this when moving between the UK and the US. The iPad localization determines things like date and telephone number formatting conventions, spelling dictionaries, and so on.
As an addendum, you can have multiple Apple ID's on a single device. This is kind of annoying to do, but sometimes it's the only way to get an app. In my case, my main Apple ID is linked to the American store, but my London bicycling maps are only available on the British store. So I maintain two different Apple IDs, and when I update my apps I have to type in both passwords and juggle them a bit.
Your mother may not want the hassle of doing that, in which case you are well-advised by @stuffe to keep everything on a single ID.
Best Answer
The App Store uses the currency of the country which you are using to access the App Store. It is not possible to choose the currency at your will, i.e. using South Korea App Store while choosing to pay in USD.
The difference is rates appears due to the exchange rates used by Apple.