8 – Change the language code for the default language

I have a multilingual website with English as the default language.

The language code for English is currently en but I want to convert it to en-US.

I have considered adding a new language with the correct language code, but I do not think this is the best solution because I have a lot of translated content, and I do not want to add all the translations again for the new language.

Is it possible to update the language code of a current language, if not, what can I do?

TL; DR
I have several languages ​​on my site and I want to update all their language codes without losing my translations.