Just extract to usual CAS mod folder. You will find the item in the masks section. If you want to change the category so to wear a different mask simultaneously, just edit the cas.ini file.
Installation
Extract the mod's .zip file to the data/mod/UserMods/CAS folder of your game directory.
Each item should have its own folder!
Installed items will show in the appropriate category of the Create-a-Skater menu.