Is there a way to select one or more tracks and assign an artist or album name to the metadata for these tracks?
Look here for information on doing bulk edits on tracks. The example shown demonstrates removing an artist credit from multiple tracks, but you can also add new artist credits in the same way.
You can also group tracks together and create a new album from them. Use the “Group Tracks” option in the Track Options tab of the Track Editor.
Thanks. BTW, why doesn’t the app change the actual file metadata when I edit the file?
By design, Roon will never modify the content of file metadata. It will read file tags, in order to help build up its own data model, but never, ever, write to them. See here for more information.