Aye its v frustrating, tried various methodical changes in Family and always crashes. I did try to edit via esf my save game where my Daimyo (Tokugawa clan) had just had a 2nd child, a daughter, and change her stats based on his son and pretty much replicate all aspects and the game loaded but then crashed on end turn and ommited the portrait from the family tree.
Did manage to change names successfully though, dug into data.pack with PFM, extracted the names and looked up what I could change them to.
Using Esf 1.4.6 which seems to not crash as often, also I have been loading a save game and then saving it as another game with esf and that seems to prevent a lot of crashes.
Anyway good luck and hope you have more succes than I
Cheers