After some fiddling (and a lot of searching) I finally found out how to change the default terminal layout for sakura in Slitaz v4.0. Other apps can probably be tweaked in the same fashion.
My wish:
To start sakura with a default screen of 100x25 instead of 80x24.
Solution:
The application is started with the settings from: /usr/share/applications/sakura.desktop.
I created a new entry there: sakura2.desktop with the following text:
[Desktop Entry]
Encoding=UTF-8
Name=Sakura2
Exec=sakura -c 100 -r 25
Icon=xterm
Type=Application
Categories=GTK;Utility;TerminalEmulator;
StartupNotify=true
Then in the launchbar I used the menu to replace the old entry with sakura2.desktop.
/emgi