I see, thx. Saving the original filenames for every KnownFile currently queued would mean to create another global met file to retain compatibility of emule's met files, I take it.
Maybe I didn't get it. I see no need to mess with met files, because file names are totally irrelevant to the network, they are just "local annoyance"

What kind of compatibility are you referring to? Functional compatibility of the feature? If that is so, please forgive me, it's been a while since the last time I ran eMule.
On the other hand we could save us a lot of trouble if besides "Clean up" we offered another context menu entry "Set to first alternative known to the network" (the final text is not the matter here :-) which would set the names of all marked list entries to the contents of the first line the details dialgog would show for each entry. If that list of alternatives works as I suspect I'd just say we don't need to store information "the network" already "knows".
Well, pehaps the full list of known network names sorted by number of occurrences could appear in the context menu?
The matter I wanted to address was really a simple one, sometimes when I am hand cleaning the file name, I mess it so much that I want to abort and revert to what it was. I really have never needed to do anything more than that.
Though, there is something that bogs me, and that is when I download a file and do not immediately check for the networknames. Then when I look again, the file is complete now I can't check the network names. This is the only situation where at least temporarily saving the network names would have some use.