This goes for dialogue and below their portrait. I'm trying to mod a specific character into the game and I have no experience with making custom NPCs, so I find it would probably be easier to just name change an NPC along with their sprite and portraits. I have all the needed resources for modding, I just need a little help on what files are required to edit.
Thanks to the changes made in SDV 1.2, all the files you need to change are those that have localized variants, in order to find the NPC's name in your preferred language, and do a global find&replace.
To change names, you got the extract the NPCDispositions.xnb in /content/data. You'll see all the characters present. You have to change where it's gray on my Abigail line (i took the " with it, but ofc don't replace that or the space after, sorry !). It won't replace the dialogues when Caroline or Pierre will say her name. It only replace the name under the portrait !