Thanks for your help and inspiration wow! o) It seems I got around making it too complicated, as this little script command does the trick.
It mainly deselects all files and then reselect them with the "MAKEVISIBLE" switch. Works like a charm here!
Btw: ReSelecting the files by the script one by one was very slow, you could sit and watch DO doing it, so it had to happen in one go by passing the collection at once.
The most difficult part then was to remember the name of that switch "FROMSCRIPT", which is not documented online, but the forum revealed it finally.
Thanks all, another leap forward to perfection! o)