Yes, this is certainly possible, and the best place to start is Part 2 of the Manual, which is all about how to design your own campaigns!

Especially relevant to changing country names is the section 3.3.2. Customize Your Campaign that starts on page 272.

Good luck with modding, and I am sure ...

Hello i wanna try and learn to make campaign on asian countries, can i change or name/ID to make custom nation?if possible can u tell me how to do it.
I Just Bought on steam this day,

wow, such a long journey mod, your doing great