Ok, actually I think I got it working.
I did it via AutoNotification, as it has the ability to use a regex to ignore the name/number of the person sending the message.
I use the intercept notification option in the plugin AutoNotification. Then I fill it with a notification from that group. However, under notification title, I delete everything except the real title and add a * behind it, so every notification title that starts with this string is selected. This seems to work.
I then just select, again under plugins, the openhab, change item, and pull a switch to on, which in turn triggers a rule, which switches the switch back off. I will try to give some information on how reliable this works.
(This requires the full version of AutoNotification, which costs about 3€)