You can add a new option for the icons setting. Icons options reside in the /usr/share/icons/option-name directory.
The option file for an icons option is located at /usr/share/icons/option-name.
The image files for an icons option are located at /usr/share/icons/option-name/icons/*.*.
The ui-category directories are apps, devices, emblems, filesystems, or mimetypes.
Typically, a new option for the icons setting is supplied as a .tar.gz file. To install the new icons option, unzip the .tar.gz file, then, untar the .tar file into the /usr/share/icons directory.
You can install your own options for the icons setting. If you install an option for the icons setting, the option is stored in the $HOME/.icons/option-name directory.