Hello again, Ralf.
I follow the process I described above just about every time I use PL. In fact, I’m right now in the middle of processing around 2,000 RAW files (from a recent trip to Sri Lanka) - with one of my steps involving renaming filenames with a numeric prefix to create a “story” told by the order/sequence of the images - - I have been doing this for (quite literally) years, with absolutely no problem whatsoever.
It does not matter that the the sidecar/.dop file contains the old/original RAW filename - - this will be automatically updated by PL. It matters ONLY that the main part of your RAW and sidecar files have exactly the same name - - AND that you close/stop PhotoLab BEFORE you rename the files.
If you have tried this in the past, and you encountered problems, then you probably had PL open/running at the same time that you renamed the {image + sidecar} files - - and this has high potential to cause problems (especially if you are renaming multiple pairs of files, and you’re using Windows FileManager to do so).
I encourage you to try the process (as described above) with a couple of test files {image + sidecar} … This should get you going again, until Svetlana addresses your wider concern.
That’s not necessary, Peter - - See above.
Regards, John M