Install
1. Backup the original cat.xnb file somewhere safe
2. Unzip the file
3. Place the new, downloaded cat.xnb file into your Stardew Valley\Content\Animals folder. This will overwrite the original old cat.xnb (so say "yes" to any pop-ups to rewrite)
Uninstall
1. Delete cat.xnb in your \Content\Animals folder
2. Put the original cat.xnb you kept somewhere safe back into the \Content\Animals folder