Okay, I figure it out. I unpacked the Main and Textures pak files which extracted into two folders One under Mods and one under Public. I took the contents to the "main" folder which was extracted to mods and placed it inside of my own Mod's folder under the Mods folder.
To clarify, upon extracting files from the paks I copied things from the below "Main" folder to the MyMod folder. I then open my mod and have access to edit all the scripts/levels/etc. which was in the Main folder previously, and couldn't be edited.
D:\Games\Divinity - Original Sin\Data\Mods\Main
D:\Games\Divinity - Original Sin\Data\Mods\MyMod