Hi Danoise!
thank you very much for your reply and your time man!
And sure, it’s possible to add static mappings too. But first there is an important question that needs answering: “where should this mapping information be saved”.
I’d say that the song comments is a OK-ish place. And I’ve got code from another Duplex app that could be used for this purpose.
So, it should be possible to add the feature “static mapping” to Duplex, but up to now it is not available, right?
About the location of mapping information I cannot give advice as I’m not familiar with the functionality, yet. I fully trust you in that point 
I naively thought that I just can map a button X to the e.g. 4th parameter of 2nd plugin of first track. This would be static enough for me as I don’t change the structure of the project. In this case, I would assume the mapping information simply in the lua-script of the controller.
Alternatively, I could use native midi-mapping of Renoise. But Duplex’ feature “pass unhandled midi messages to Renoise” seems to not work for me (I posted this issue here)