Are Citibank, Bank of America, discover card, and capital one available in South America region (Brazil) of App Store? Need to switch regions but cannot lose these apps. Thanks Jamison

1. The Apps will probably not be available outside of the US App Store , since they are US only financial institutions except for Citi which does operate in many countries outside the US. However, the Citi apps in other countries will be the local apps for their local branches and not the US version for U.S. based accounts.
2. Downloaded Apps on the iPhone will not be removed by changing regions. They will continue to exist on the iPhone and should work normally until an update is required for them that renders their current version unusable. Since the App won't be available in the Brazilian App Store, there would be no way to update them.
3. Unless it's absolutely necessary to change the region for Brazil for some reason, I would keep the iPhone in the U.S if those apps are required. Consider a secondary iPhone for Brazil apps, with a Brazilian Apple ID instead.

Phil0124’s advice is sound.

Keep in mind IF you change your AppleID region you also have to have a Brazilian payment method.

It’s not that it’s particularly hard, but depending on your circumstances it might not might be a task you want to take on.

See exactly what’s involved here:

Change your Apple ID country or region - Apple Support