The only way is to use one of the pre-programmed, but unused culture tags. Byzantine and Iberian come to mind. I've used them before in mods, so they work. This is unless you need a "dark" culture, then I am not 100% sure which tags are unused, but I am sure that someone does.
Remember to use something like notepad or notepad++ to edit the files.
So, to make Iberian into Swabian edit the world_names.csv, under cultures change:
Code:
CULTURE_IBERIAN;Iberian;Ibérien;iberisch;Ibérica;Iberica;;;;;;x
to
Code:
CULTURE_IBERIAN;Swabian;Ibérien;iberisch;Ibérica;Iberica;;;;;;x
Then in the character_names.csv add Iberian entries between Hungarian and Irish like this:
Code:
hungarian;male;Zsigmond
hungarian;male;Zsolt
iberian;female;Helga
iberian;male;Otto
irish;female;Affraic
irish;female;Aíbinn
So, remember to use the culture, not the name (so if you use the Byzantine tag, place Byzantine where it belongs alphabetically and even if you rename it "Native American", the proper tag is "Byzantine".
Then to add your culture to the map, edit the province file in the scenarios folder changing the proper provinces to your culture. Add do the same to the characters file in the same folder.