I am not a modder but I assume you have to do the following...
1. Map out each country and assign the proper province IDs. (existing countries and countries possible.) (This would include unit placement and such also)
2. Go through all country specific events and change events related to provinces.
3. Make any necessary or desired prov. information for map such as base levels, resources, aa, forts, etc...
4. Then there would probably need to be some beta testing to see if the game is still balanced and all events fired as desired.
It would be alot of work in my opinion, but worth it in the end. Maybe you could get help from the community to modify it, or maybe someone is working on it already.
Another idea is to take the full DH version mod and modify a copy of it slowly by changing each file as needed to include the changes. Atleast this way you can do it in smaller steps and test the changes as you go.