[DayvG]

Fuse 46 is for ACC not KAFAS2. KAFAS2 should be spliced/connected to fuse 44. I use an online ETK, bimmercat is my ETK of choice. All the parts you’ll ever need are right there. F44 is KAFAS2, F46 is ACC. I don’t think the second row is for adding second/additions connectors as the connector itself is what the fuse plugs into, however I could be wrong with the addition of the tap fuse in that socket. I’ve never actually fitted one

Seeing the photo attached, I came to conclusion that to get 2 rows working, you need to put 61136937069 into main (deep) row, then you can attach 61138377730 in the second upper row.
61136937069 is longer than 61138377730 and in that photo you can see that where both rows are utilised, the metal element around the wire is elevated.
Therefore this is probably most "BMW" approach to add new wires- replace original wire with new with clip, then put the old one in upper row, connecting it to the clip of new one.

I wish I knew that before

One last question: where are you buying new wires which you need to add for all the retrofitting?

Thanks for all your help mate!

You are 100% correct, just had a look at some spare parts. See pictures.