Well, I was able to locate the family members, find "Fredericka Louisa", rename her, give her a new portrait, change a value that I thought was gender (on all male family members it said "True", and on all females "False") and alter her age, but when I did my king just wouldn't die. I had a save game from the year before he died (at the age of 69), and every time I ended the turn he would die, no matter how many times I tried it, until I edited the save and then he miraculously lives for another five years (after end-turning ten times I stopped... I don't know for sure if my changes made him immortal, but it seems likely). I thought maybe he was dying because his heir was 63 (old), and so the game wanted her to become queen and sire heirs before she died, and therefore when I changed her age to 43 that gave the king more time, but I tried editing the details and leaving the age the same and the king still became immortal.
Probably I would have an easier time if I downloaded your mod, which I really should have done by now and will do promptly now that I think of it.