The Resource Path
IceWM looks in several locations for configuration information, themes and customization; together these locations are called the resource path. The resource path contains the following directories:
$ICEWM_PRIVCFG; $XDG_CONFIG_HOME/icewm; $HOME/.icewm The first of these which is defined and existent is used to search for the user’s personal customization.
/etc/icewm the system-wide defaults directory
/usr/share/icewm OR /usr/local/share/icewm the compiled-in default directory with default files
The directories are searched in the above order, so any file located in the system/install directory can be overridden by the user by creating the same directory hierarchy under $HOME/.icewm.
To customize icewm yourself, you could create the $HOME/.icewm directory and copy the files that you wish to modify, like preferences, keys or winoptions, from /etc/icewm, /usr/share/icewm or /usr/local/share/icewm and then modify as you like.
To customize the default themes, create the $HOME/.icewm/themes directory and copy all the theme files there and then modify as necessary. Each theme has its own subdirectory. Themes can be downloaded from https://themes.ice-wm.org.