Thanks for reading, I was wondering how I can edit an existing country, essentially I want to take Germany, change the Generals' stats, add one or two cores, mess with the traits, and make Plan Z and U-boat effort not exclusive. I just want to make minor changes. Do I hit create country and then just make the tag as GER? Any help would be greatly appreciated. 

Personally, for that, I wouldn't try using this site for that, as there will be a lot of extra things you would need to do, as the site currently doesn't do full imports/edits for countries.

I would copy the relevant files for what you need to edit from the base game to your mod's folder (keeping the same folder structure, so focus tree is copied to YOUR_MOD/common/national_focus, for example) and make the changes in there.

The file locations are: (with extensions, these may be hidden by default on your OS)

Hearts of Iron IV\common\national_focus\Germany.txt <- The focus tree. You can do CTRL+F (CMD+F on Mac) to find "Plan Z" and "U-boat" and remove the mutually exclusive line from them.

Hearts of Iron IV\common\characters\GER.txt <- This contains generals, along with other characters (leaders, advisors, etc.). Once again, find the people you wish to edit. And then look under the following "corps_commander={" for army leaders or "navy_leader={" to edit traits/skill levels.

Hearts of Iron IV\history\states\STATE_ID - NAME.txt <- These are the state files. You could use the site to export these if you don't wish to mess around in these files. As long as the country you created has the tag "GER" it will work.