No, i didn't need to. I did as normal. The icon-themes are stored in separate sub directories under "/usr/share/icons/".. Theme Customizer take advantage of that. You have a file called gtkrc witch tells the system what theme and what icon-theme to use. So first you chose the theme, the normal way, and then the icon theme through Theme Customizer. The only "special" thing with Actus Reus is setting that theme up. You need to store it and symbol link it correct. You can find gtkrc under "/etc/hildon/theme/gtk-2.0/gtkrc".