X11 global settings xauth / xhost option

Dear Folks,

i want to display
messages time and event triggered on a group of machines
as root with “xmessage”.

Where do I have to insert the “xhost +local:root@localhost”
I want it to be set, no matter what user is logged in
and what settings are in local .xsession/.xinirc files.

where is good documentation on suses way to startup x11 and reading / overwriting session settings?