Okie Dokie I managed to get my hands on a PC with Excel installed. This is what I've done:
* Made a copy of all the Main.Pak files
* Unpacked them with lstools
* Opened Character.xlsm in Excel, made changes, saved file.
* Opened All.xlsm in Excel and clicked Generate.
* Copied the new 'Stats' folder to my Divinity-Original Sin/Data/Mods folder in the root directory.
It doesn't seem to work

I tried it with an existing save game and a new game. But no joy.
What did I do wrong?