Who are you changing, to what culture?
Also check Documents/Paradox Interactive/Crusader Kings II/log/error.log if there is a relevant error message.

I did a little bit of more testing, and the game crashes only when I tried to creat a custom female ruler for Ostfriesenland county. When I customize other rulers it works fine, even if I change their culture to frisian. And the error log is very long but I can't find anything related to this mod (plus I am a noob when it comes to reading those kind of files). Well, i suppose I doesn't matter much since I just disabled the mode while I made that character and than resumed playing it with the mod enabled just fine.

Will be fixed.

Can confirm the same thing happens if you try to create a female ruler in svipjod at 867 start.