xfce4-panel changing icon for showdescktop plugin

[Sylvain]

Hi,

I may have missed some documentation but I just want to change the Icon
displayed in the panel.

Can I do something like copying the showdesktop.desktop file somewhere
to ~/.config/xfce4/… or something, then edit it to point to another
icon. And that's it?

Could you point me to the right path I need to look after?
Or the good documentation URL.

I've found:

http://forum.xfce.org/viewtopic.php?id=7671 - [Solved] 4.8 Panel
backgrounds...
~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-panel.xml
http://docs.xfce.org/xfce/xfce4-panel/preferences - modifying panel globally
http://docs.xfce.org/xfce/xfce4-panel/theming - modifying theme
https://wiki.xfce.org/dev/howto/panel_plugins - dev wiki

and

restart the panel
xfce4-panel -r

https://mail.xfce.org/pipermail/xfce/2013-June/032350.html
xfconf-query -c xfce4-panel -l -v

Nothing helped in that way for now.

Regards,
Sylvain.