1) unarchive the materials & models folders into steamapps/common/Counter-Strike Global Offensive/csgo/
2) BACK UP PAK01_DIR.VPK IN CASE YOU SCREW SOMETHING UP!
3) open up pak01_dir.vpk in Notepad++ or some other proper editor
(Regular notepad will probably break your pak01_dir.vpk, so don't use that)
4) Use find & replace to find all instances of v_knife and replace those with
anything else, say, v_knyfe for ease. What this does is basically it points the
VPK to a file that doesn't exist, and forces it to load loose files - ie. my model/textures.
5) Go in game and enjoy!
How to uninstall:
Restore backed-up pak01_dir.vpk. You can delete models/weapons/*v_knife*
and materials/models/weapons/Kosai106/, if you so wish. Not necessary, though.