You can try with the guest-session-prefs-lightdm kit.
README File:
guest-session-prefs-lightdm is a convenience kit that makes it easier
for a system admin to configure the guest session feature provided by
the lightdm package. The preferences are set via shell commands in
these two files:
/etc/guest-session/prefs.sh
/etc/guest-session/auto.sh
The kit is shipped with the settings I made on my own computer. Some
may share my preferences, but most admins who install
guest-session-prefs-lightdm will probably make changes and/or
additions to those settings.
My aim is to give the admins options, and the framework the kit offers
for configuring guest sessions may be of greater interest than the
particular settings that I happen to like. Still, my code snippets can
serve as models.
See also http://ubuntuforums.org/showthread.php?t=1566078
I would suggest that you install guest-session-prefs-lightdm as is,
and take it from there when you have reviewed the resulting changes in
behavior.
Ubuntu 12.04
1) Go to this page to download the guest-session-prefs-lightdm-0.12.tar.gz package to your ~/Downloads folder.
2) Open a Terminal window and type:
cd ~/Downloads/
tar -xf guest-session-prefs-lightdm-0.12.tar.gz
cd guest-session-prefs-lightdm-0.12/
sudo ./install.sh
Note: The script install.sh will tell you if you need to install any package to complete the installation. eg (gettext)
3) Edit the /etc/guest-session/auto.sh file to add the command to resize the Launcher icons.
sudo nano /etc/guest-session/auto.sh
Add the following lines to the file:
# Change Launcher icon size to 32
gconftool-2 --type int --set /apps/compiz-1/plugins/unityshell/screen0/options/icon_size 32
Save the changes with Ctrol+O then Enter and Ctrl+X.
**4)**Finally you can lOgout and login in the guest account to see the changes.
Result:
Ubuntu 12.10 & 13.04
Thes steps are the same as 12.04, the only change would be the command to resize the icons.
Use:
# Change Launcher icon size to 32
gsettings set org.compiz.unityshell:/org/compiz/profiles/unity/plugins/unityshell/ icon-size 32
instead the gconftool-2 command.
NOTE: This kit by default has examples like display an info dialog, or create a link to a folder. You can change it according to your needs.
Hope this helps.