Called also LH and they confirmed that it would not be considered as a stop, but that I had to go via the travel agency to modify the reservation.
This morning asked our secretary to contact travel agency and give them my feedback.

Secretary came back : travel agency is very upset that I contacted LH directly, they stick with their story, now say that it might be possible if LH in Germany (?)would agree.
I am fed up with it, told secretary to just leave it as it was. I will take the risk of missing my connection on monday.

Luc