Files corrupting after modding a father in save file, safe way to do this?

I'm playing a female ruler and AI keeps denouncing my bastard children, so they end up fatherless. No info is shown using the real fathers command either. I have tried to get a father to appear in the family tree for these kids using a 'natural' visit chambers, a Sins Visit Chambers submod interaction and also pollinate. Nothing is working and they are poor fatherless children.

I have tried to mod this myself by adding

father=[char ID of their dad]

but it keeps on crashing or corrupting the entire save game so the loaded game file shows as 'no character' for all of Westeros.

Can someone advise me on how I can get the fathers shown?