OK, so my common/dynasties.txt overwrites all dynasties instead of extending them (no, I don't have replace = "common" in the mod file). My change of holders for c_ulster doesn't take. And my added localisation file doesn't work.
All I have in the mod file is this:
name = "New Guy In Ireland"
path = "mod/NewGuy"
... which, based on what I've read, should mean that everything in there just extends what's going on. What am I missing?
"Extend" means that only files which you put in the mod directory are changed (and if you changed dynasties.txt to include only 1 dynasty - that is what you will get) or added (if you include brand new files). The rest of the files are used from vanilla.
"Replace" means that the whole content of given path is wiped out: in your example, every single file in CK2 vanilla directory would not be used and instead the mod would attempt to use files in the mod directory. If you made, let's say, replace [path = "mod/NewGuy/history/characters"], the mod would not use ANY of the vanilla characters and instead use only yours.
I hope that helps understanding extend vs replace.
EDIT: Let's take another example.
I made a mod to include Swiss culture, characters and culture-specific pikemen buildings for them.
Since the provinces I chose to make Swiss were previously German (Valais, Neuchatel, Aargau, Bern, Schwyz, Grisons, Chur, St. Gallen) and had German rulers, I had to change the history/characters/german.txt file (I exempted the count of Grisons from this Swisserlization since he was an Italian vassal and not German).
So now there are two ways I could have done that: (1) change just the german.txt file and re-brand all of the chosen characters from
Code:
culture="german" to culture="swiss"
and put it into the mod directory or (2) remove the chosen characters altogether from german.txt and put them to a new file swiss.txt with the changed culture as above and then put BOTH files in the mod directory.
Both ways work, and in both ways you have to change german.txt to include or exclude what you want but you have to leave all the other characters in place.