Easy & Fun
Launch MiLife Holidays and click the Install button for whichever theme you want. Then click 'Launch MiLife'. (You may need to select the 'Silly' window theme in MiLife's preferences to see your new theme).
Restore
When the holiday seasons are over, you can easily restore MiLife's original 'Silly' theme by clicking the Restore button.
Happy Holidays
This program is free.