hi guys,
finally I did it. I customized kde menu after a remaster. The solution I found sounds me like a sort of workaround, but at the moment fits well what I was looking for, a new (smaller and with new items) kmenu.

I booted from the live-cd, then custmized (graphically, with the kmenu editor) kde menu since I liked it.

I saved /home/knoppix/.config and /home/knoppix/.local directories in a usbpen (a floppy or a hard disk partition is obviously the same, these files are saved to be reused after you stop the live session.

Then I rebooted to my linux hard drive installation, where I store all files that will be the remaster, and copied the .config and .local directories into /etc/skel (in the copy to remaster).

Edited /etc/X11/Xsession.d/45xsession, added ".config" at line 64:
Code:
***before***
rsync -Ha --ignore-existing /etc/skel/{.acrorc,.Xdefaults,.gimp*,.gconf*,.bashrc,.nessus*,.links,.local,.lynx*,.qt,.xine,tmp} $HOME/ 2>/dev/null
***after***
rsync -Ha --ignore-existing /etc/skel/{.config,.acrorc,.Xdefaults,.gimp*,.gconf*,.bashrc,.nessus*,.links,.local,.lynx*,.qt,.xine,tmp} $HOME/ 2>/dev/null
After the remaster and a boot into live session, I found my new kmenu for the knoppix user

don't forget to set read permissions ("chmod -R 644 .config .local" inside /etc/skel will do the trick) or your changes will not be reflected to menu structure.

here's the config of my .config directory:

Code:
.config
`-- menus
    `-- applications-kmenuedit.menu             [menu structure description]
and this is the .local's one:

Code:
.local
`-- share
    |-- applications       [folders applications]
    |   |-- Bourne Again SHell (bash).desktop
    |   |-- C-Shell (csh).desktop

    ....(other apps)....

    |   `-- xmms.desktop
    `-- desktop-directories      [menu folders]
        |-- Disks.directory
        |-- Network.directory
        `-- kde-internet.directory
I hope this could help someone,

-- Lorenzo