If you want to go one step further , you need to manually mod a saved game (or you can use the hoi2 editor that comes with the game).
All I am going to tell you is that you can find your saved files in /programfiles/paradoxinteractive/hoi2/scenerio/saved and look above ; clicking "show compatibility files". If the file is "read only" , unclick it by right clicking the file and unchecking the box under "file details".
You will notice that everything is slightly explained using comments.
To start , use ctrl+f and look up the country you want to mod by using the command
So for example my country could be
For the United States.