Help me understand how Apple Music Cloud Library works regarding metadata

So I just found out that you can edit the metadata of music downloaded from Apple Music into your library. As someone who spent hours curating their music pre-Apple Music, this is awesome to understand.

I have two questions:

  1. For music which I have only ever downloaded from AM, if I rename the Artist, for example changing ABBA to Abba, will this new naming be maintained for songs I download for them in the future, or do I have to change it on my Mac every time moving forward?

  2. For my local music that had its metadata “destroyed” (mainly album art, collaboration artist name and album names, e.g. adding unnecessary info in parentheses) when I first turned on cloud music library - can I resolve this by manually updating all affected music in the AM app on Mac? Or will the AM info eventually replace my local music even if manually updated?

Thank you!