Asset question on unreal engine 4 dev kit for conan exiles

Im trying to cook my mod, and right before it saves, but unable to save the foliage type of any of the assets included with the dev kit. Im just new to all of this been working on it the last week, trying to learn as much as I can, when i played the previous mods that didnt save the information, they would just crash when ever you tried to pick up something, as i realized because it cant save the files to the mod, mainly because they are already in the base game, and were not changed, so what im asking is am i able to use these assets in my mod? if not it seems odd that they are even on my hardrive, im sure im missing something, hoping someone could enlighten me. Thanks.