Good afternoon, Gert Schneider 

If I translate your request correctly:

"Is it possible to program a midi interface, midimap, via extend?
I want to call Midimap from a program, select the output device and send data there."

Depending on the language this interface is written with, you can work with either Java or .Net from an ACUCOBOL-GT application.

Initial information are available here:

extend Programming Guides > A Guide to Interoperating with ACUCOBOL-GT Version 10.5.1
https://www.microfocus.com/documentation/extend-acucobol/1051/extend-interoperability-suite/GUID-0617E68F-C102-4A3B-9797-279F653777D7.html

I suggest you to contact your local Technical Support, if you need further help with these functionalities, by submitting a Case in the portal - https://portal.microfocus.com/

Regards.