Little lat for an answer and I am not sure if I understood you correctly but I was able to respec NPCs' stats e.g. Durances' without problems (so they keep their new stats after reload).
What I did, probably basing on similar tutorial, I extracted files from companion***.unity3d edited, imported back and replaced.
I am completely newbe to this (and game btw), but I desired to edit some thigs and found that reddit page. And I just wanted to tell you that this reddit procedure worked for me like a charm.
For attributes anyway, because I did not notice any changes when I wanted to edit skills/skillbonuses.
I have used 32bit version on Windows 10.