I believe this will also work in S10... I have a doc on this from long time ago, I think from Sun, but it refered to a bug in s8 and s9, however, theses files still exist in the same location in S10, so it should work. I think the bug was fixed in newer versions of S9, but this can also be used to lock down a system as you intend to do, not necessarily what the bug was initially about.
# /usr/dt/bin/dtconfig -d
and then stop the currently running dtlogin:
# /usr/dt/bin/dtconfig -kill
If XDMCP remote session access to a machine is not required at all, but graphical login access for the console and/or Sun Ray devices is required, dtlogin(1X) can be configured to not listen for XDMCP connections by editing the "/etc/dt/config/Xconfig file" and removing the "#" symbol at the beginning of the following line:
# Dtlogin.requestPort 0
If the "/etc/dt/config/Xconfig" file does not exist, create it by doing the following:
# mkdir -p /etc/dt/config
# cp /usr/dt/config/Xconfig /etc/dt/config
# /etc/init.d/dtlogin reset