At the title screen, copy and paste them in the bonus code button,
after you activate the items in your avatar so you can put on your
boots.

Code Effect
———————————————————————
Best-VA – Unlock April Fools „High-Quality” Voice Acting, you can
also disable voice by re inputting the code again.
Holiday-Man – Unlock Holiday Man Christmas quest.
WoN-Boots – Unlock sparkly boots.
(decent stats, mostly fun for the on-screen effects)