Many thanks for the above.
First of all: I had no idea that one could create a personalized grp.
Over the last hour, I went back and forth in the online manual.
Then searched for the Opus 13 reference manual (pdf) but I believe there is none.
Found and downloaded the pdf from: DirOpus 13 Manual PDF
with thanks to @StevenEdford
Vainly searched there for something that resembles to create filter group.
Let it rest.
It is not worth spending so much time on this.
Thanks again!