First I want to thank you all for your answers. Sorry, I was quite a bit busy the last weeks, so I haven't found the time yet to work it all out.
I copied ~home/AppData\Roaming\calibre into ~AppData\Roaming\calibre_old and compared the directories. Most of the files are different, but I'm wondering if the settings are in .py or .json files.
However, I found a file in metadata_sources\global.json, content is
{
"swap_author_names": true,
"ignore_fields": []
}
after I copied this file over in the current Directory of calibre, it's now swapping the author names again
Maybe thatwill help other ppl also, since I found some requests regarding that surname/prename changing...