It is actually rather easy, in the sense that even if the game spots issues (like provinces owned by two states) it chooses one option automatically and doesn't crash.

Go to C:\Steam\steamapps\common\ImperatorRome\game\common . Needless to say, make a backup of the files you're gonna be testing.

There is a text file called setup, there you'll find all countries and what provinces they control.

Let me take it slow and make you a simple guide to create a new state:

Say you want to create Lydia. You need to open the countries.txt, and choose a three-word ID. We're gonna use LYD, because it's not used by any other state already in the game. You're gonna type LYD = "countries/anatolia/lydia.txt"

Afterwards, go to that folder countries/anatolia, make a copy of one of the texts already there and name it lydia . Inside the text, you can edit the rgb colour to change the colour of your new state.

Now that your new state Lydia is ready, you're going to open setup.txt, and you'll notice that it contains all the diplomacy and which provinces each state owns.

That's how the entry should look:
LYD = { #Lydia
agressive_expansion=10.000
government = aristocratic_monarchy
diplomatic_stance=appeasement_stance
primary_culture = macedonian
religion = roman_pantheon
monarchy_religious_laws = encourage_cults_monarchy
monarchy_legitimacy_laws = reminting_policy

capital = 292 #Sardeis

own_control_core = {
279 285 278 #aeolia_region
274 275 292 293 296 298 299 300 301 305 307 308 #lydia_region
287 288 289 290 291 294 1969 1972 #ionia_region
295 1947 1962 1966 #Caria_mediterraneus_region
273 304 306 #mysia_abrettene
}
}

Notice that the #symbol is simply a note you've made, it isn't read by the game. Assuming that I want to remember that the capital with the ID 292 is Sardeis, I simply type #Sardeis.

Make sure the provinces you've allocated to Lydia have been removed from their original owners. For this reason, always use cut-paste. Find the provinces you want to take away, say from Phrygia, cut them and paste them to your Lydia entry to ensure that they're not owned by two states at the same time.

Finally, go to game/localization/english and open countries_l_english.yml or whatever your language is with notepad and type:

LYD:0 "Lydia"
LYD_ADJ:0 "Lydian"

or whatever you want to name your state and its adjective. If you have another country, like Pisidia, and your ID is PIS, you're gonna change the entries accordingly, like
PIS:0 etc
PIS_ADJ:0 etc

Oh thankyou so much. I looked at that file and passed over if because I failed to notice the provinces/cities.

No problem, also bear in mind that ingame, if you select the political map mode you can hover over provinces to see their IDs. This makes it very easy to check which provinces you want to allocate. You can even keep your setup.txt open and save it while your game is open, it won't crash.

Originally posted by menkalinan:

No problem, also bear in mind that ingame, if you select the political map mode you can hover over provinces to see their IDs. This makes it very easy to check which provinces you want to allocate. You can even keep your setup.txt open and save it while your game is open, it won't crash.

Sorry if I am reviving a somewhat dead post, but I just wanted to add that if you save while the game is open, go back to the menu, and go back into the game, things will be been changed without having to restart the game.