We are not really happy with our floor-to-ceiling windows (140cm wide, 2 sashes), especially on the first floor.
My question therefore: Is it possible to convert them afterwards to fixed glazed at the bottom – casement at the top? And preferably without tearing the frame out of the wall. So to speak, just "clip in" a fixed system at the bottom?
The word you are looking for is "transom".
No – you cannot "tinker" afterwards; you must have the entire window element replaced.