Woo hoo! Off to a good start...
<button>
<type></type>
<text>test</text>
<description>this is a test</description>
<action>EXEC msg_client.py --msg "test message"; xterm -e bash&</action>
</button>
Displays message "test message" and opens a terminal in a new window.
I did this the "wrong way" by directly editing /usr/share/mythtv/themes/defaultmenu/mainmenu.xml but now I've found the theme chooser and will read up on themes and make my own (and revert the default theme xml files to their original state.)
To load it, pressed F3 to get the terminal (I think LinHES calls that "tilde") and ran "sudo killall mythfrontend". It reloads by itself a few seconds later.
Editing files in a separate ssh terminal for more screen "real estate."

At the moment, I am running LinHES under VirtualBox on my Windows laptop, to get familiar with it without making a mess of the actual machine I will be installing it to. (Used port forwarding so I could ssh to it.) So no actual tuner cards. That's OK, the tuners were found when I initially installed on the "real" hardware.
I'm not new to Linux, but I am new to Arch Linux. For my own machines, I've generally used some flavor of Ubuntu. At work, I'm used to Redhat, and long before that, Solaris (not Linux, but still *nix.) So getting used to pacman instead of apt.
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Not using LinHES because 8.6 didn't support my hardware, but still very interested in future developments, so lurking once in a while.
