I assume you can still play an European battlenet account in South Korea? Just not on the South Korean servers? Unless they go out of their way to block people.
Presumably not the good old physical authenticator? Speaking of which, that thing has an astonishing battery lifetime.
When that dies the only option is the bnet app. I have the physical one too but someday it will die.
What i was talking about are people who need a valid country change to match a phone number on a bnet account and cant because of the korea account restrictions. It is a low number in that situation.
Got an unused spare, bought some years ago as I couldnt understand how the first one was still alive. D5, maybe even D6, will be out before I run out of physical authenticators! 
Unless they have removed the ability to register the physical authenticatorsā¦
Yes Blizzard, I do have phones, plural. Doesnt necessarily mean I want to install your stuff on them 
Here is the fine print from the email that Newegg sent me with the code:
āOffer valid only through authorized ETAIL and Retail partners. For redemption instructions, here. Offer may not be substituted, exchanged, sold or redeemed for cash or other goods or services. Customers are responsible for any applicable sales tax. Offer may not be combined with any other offer, Game Time card, rebate, or discount coupon. Product subject to availability, quantities are limited. Retailers, distributors and employees of NVIDIA and Blizzard and their agencies/affiliates are not eligible. Void where prohibited. Offer code will be provided and redeemable to customers with the purchase of a qualifying NVIDIA product. Bundle must be redeemed with a qualifying graphics card installed. Customers must meet the age requirement of 17 and up to redeem. Regional/Country Requirements- Some codes require that they be redeemed in specific regions or countries they were purchased in. Please redeem the code in the appropriate region/country. Please check carefully the description of the product on the Retailers website or in store to confirm that it is part of the promotion.ā
So yeah I guess maybe not every code is region specific but there still exists region specific codes.
Putting an auth on the account now requires a valid cell number matching the country of the account.
So can i use a code and install the game on other pc that not have rtx 40xx?
The game key is tied to your Battlenet account once you claim it, not the computer. Once you have claimed the key on your Bnet account you can install the game on any PC you want.
Just put the Blizzard Desktop App on the other computer. Log in with your Battlenet account. Click the Install button.