Please help with Mod on un-encrypted historical museum App made in 4.18

Hello, I am looking to mod an app that was free software (and is now abandon-ware). I only want to change a couple things for my purpose (and that of my nieces and nephews. So they can experience it ,… better,…) I am not looking to ‘release’ etc.
I can unpack the pak, turn all cooked assets (back) into meshes, textures, sounds, etc. I can make any changes I need to the Textures, and a mesh etc,. , the only thing I can’t do it get the game to run when I try to mod it, Whether I try to Re-pak (problematic!) or not, I always get:
*‘c:/users/Woody/AppData/Local/Stage9/Saved/Config/WindowsNoEditor’ must exist and contain a DefaultEngine.ini’

a*nd even though I triple check there is a Folder called WindowsNoEditor and an Ini called: DefaultEngine.ini, I am never able to make even the slightest change!
Help would be so very most welcome!