change "desktop access" icon

[Bojan]

Hello, I am trying to change the "desktop access" (or "show desktop")
icon, through configure files. In my kickerrc there is an etry:

[DesktopButton_1]
FreeSpace=0

which corresponds to this button.

I was thinking I could do this:

[DesktopButton_1]
FreeSpace=0
StorageId=:showdesktop.desktop

And then in ~/.kde/share/apps/kicker

create a showdesktop.desktop file. However, I am not sure how to
create the desktop file. For example here's my firefox .desktop file:

[Desktop Entry]
Comment=Mozilla Firefox Web Browser
Comment[en_US]=Mozilla Firefox Web Browser
Exec=/usr/bin/mozilla-firefox
GenericName=
GenericName[en_US]=
Icon=/usr/share/icons/crystalsvg/scalable/apps/firefox.svg
MimeType=application/vnd.mozilla.xul+xml;application/xhtml+xml;text/html;text/xml
Name=Mozilla Firefox
Name[en_US]=Mozilla Firefox
Path=
StartupNotify=true
Terminal=false
TerminalOptions=
Type=Application
X-DCOP-ServiceType=
X-KDE-SubstituteUID=false
X-KDE-Username=

However, "desktop access" is a special button and not an application,
so I am not sure what are all the keys for a special button, and the
exact format of the .desktop file for a special button. As well I
don't know what's the Exec line for "show desktop" suppose to be. I
have searched all over my computer for the .desktop file that defines
the "show desktop" special button for all users, but I can't find it.
If someone can tell me where it is located, it would help a lot, since
I could just copy that and modify it as needed.

Any suggestions on how I can change the "desktop access" special button
icon are welcome.

Thanks a lot,

Bojan