Slitherine

I found that the unreal asset in a mod folder will not be loaded like csv or campaign files, I create a new portrait for briefing and it works when I directly puts it in the game folder, but it doesn't work when i tried to load it as a mod,
Any way to solve it? Or maybe now there is noway to load unreal file by using modding support but only can be done with change or adding to game file itself?