Need help model swapping Agent 47's model.

I’ve been wanted to mod a custom character over Agent 47’s face, I’ve looked through guides and these forums and I thought I made the mod correctly. But when I use SMF to import it into the game it corrupts one of my game files and I have to verify the file integrity before the game will open properly again (Will crash when trying to load into the main menu)

How have I managed this and any help would be greatly appreciated <3