Changing Iconsize in .desktop

Hello,

I would like to change the iconsize on my gpe-system. All files are of
newest versions.

According to my understandig, I can start mbdesktop with the cmd-line-arg
"--iconsize 40" or I could insert a line in
/usr/share/applications/.desktop, which is what I did, as I did not find
the script which invokes mbdesktop while starting.

My system recognises and parses .desktop but reports an error, obviously
due to a wrong syntax.
I tried one single line "iconsize 40" and "iconsize=40", both didn´t work.

Does anyone know the proper syntax or the shell script that invokes
mbdesktop for the first time?

Thank you for any help!

Hajo