I need to add/edit some countries to this list but cannot find any way to do it. googling only return post form 2016 or earlier saying its impossible.
Which version of Magento are you using and which countries are not present into that list?
There is a public function getAllOptions() which returns the array of all countries.
You can add your logic in this function.
If you are using Magento 2, you can get this function from the following path.
If you are using Magento 1, you can get this function from the following path.
Note: Don't add your logic in the core files. Override this function in your custom module and then add your logic there.
What logic? Nothing in that function looks like a place where i can change "Hong Kong SAR China" to "Hong Kong". the country of manufacture attribute does not have the "add option" button and i cannot click anything it's all grayed out.
Ex1 is the color attribute with a working add option and i can use all fields
Ex2 is the country_of_manufacture attribute where i cannot change anything. I am an admin