So I made all my old MP3s from ancient times hidden in Roon, because I really don’t want to listen to them. But I don’t really want to get rid of them either, because memories.
iTunes makes it easy to see which ones are bad, so that I can replace them. But is Roon smart enough to unhide them once I do? I.e. does it detect it’s a different file? And does it even care because it’s the same song?
Hi,
When you add the lossless version of the albums Roon will treat them as separate entities and will display them.
It will leave the MP3 versions still hidden.
I know this pain, too. 
I think Carl’s given you what you need here, but let us know if anything’s unclear.
Thanks, very clear.
Another related question popped up: what happens with playlists that I’ve made with lossy versions once I add lossless versions of the tracks? Since Roon figures out it’s just another version of the same track/album and makes the new one primary, will the song retain its place in all my playlists?
No, playlist entries are fixed – I can see a few cases where I’d want some automatic behavior, but I can also think of a number of cases where the behavior could be really confusion and ambiguous.
When you upgrade an album you’ll need to replace playlist entries manually, but you can see which playlists a song is part of from the Album screen.