I created a mod with some new regiments before to include Brazil and Mexico WW2 markings... it is not as easy as you think. I mean, it is time consuming, not so much difficult. You have to find which files to modify, do some java programming so the engine recognizes a new country, then you have to come up with country names, digraphs, then rehash, then you come up with regiments, enter them in a few INI/properties files, then you have to create the TGA graphic files in the right format/size paying attention which areas are transparent, and then finally you have to create some associated flat text files to associate with the new markings and regiments... and hope that the coding was done in the right java files, because the countries are distributed across a bunch of them. Form my mod there were 4 java files... all in all, the mod had 2,438 files in 59 folders at about 115MB... just to include two countries and a few regiments for each...
SAS~Malone is pretty right...
It is not impossible, but you gotta take a couple of days of doing nothing else... you start going a little crazy after a while.