Thanks again, Iain!
As an IT-guy, I was used to use macro's in the past very often, mostly to work around an inability of an application. Before I start with that I need to confirm that it's an inability for sure, because the best way always is the direct way. So, I still hope that there is a direct way to solve this
The possible 2 workarounds I consider:
1. modifying a configuration file like "OrganID001292Config.OrganConfig_Hauptwerk_xml" in this way:
a) replace the last used combination set or favorite #1 by the set I need (e.g. with a perl command).
b) call the last used combination set or favorite #1 with a MIDI command (this is an existing HW trigger).
2. create a macro that 'understands' a text string representing the unique name of the desired and to be opened combination set. This macro should ideally be able to select the matching combination set from the HW option list.
In both cases I need to be able to send from my score reader a MIDI command containing a unique ID for that specific score, like the name. I still have to figure out how that works for forScore.
Assuming the forScore challenge will be solved, next problem is to make the HW machine understand that the incoming MIDI command has a variable text which should be put through some macro application.
For that you mentioned Bome. A quick scan learned me that this might be a rather complicated solution, so I found another app: Keyboard Maestro (for Mac OSX). This macro app understands MIDI by its own and can translate the code to an action.
Summarizing: I still need to find out a lot, but eventually I should be able to find a stable solution.
Your ideas are still highly appreciated!