to change catorise icon to your own icon use filebox & go to this path...

usr/share/icon/hicolor/64x64/hildon

the path above is the default path for all catorise icon...you need to change these icon (remember to make backup for these icon aswell)....

app_install_all.png
app_install_desktop.png
app_install_development.png
app_install_education.png
app_install_games.png
app_install_graphics.png
app_install_multimedia.png
app_install_navigation.png
app_install_network.png
app_install_office.png
app_install_other.png
app_install_ovi.png
app_install_science.png
app_install_system.png
app_install_utilities.png

change these icon but remember the icon size must be at 64x64...

here is the example after i have change the catorise icon on my n900....