Does iTunes Match/Apple Music change the data that I have manually input into my songs?

So I have this big question: will it mess up my library organization again???

Yes it will. Match looks for the matching copy in the iTunes Store and uses that with its metadata. It does not attempt to copy the metadata changes you have made.

Match is not supposed to mess with your local library, unless you delete a local copy and download the matched copy. But sad stories abound.

Hi Arthur,

Match does not automatically replace the copy in the local library on your computer. It only makes the matched copy available to your devices.

If you wish to have the matched copy in your local library (for example, to replace a 128 KBPS file you got from Napster in 1999), you have the option of deleting the local copy and bringing down a matched copy. That process is triggered manually, not automatically. However, based on what I see on the Forum, it is possible to do it inadvertently.

Here is a pretty good article about how Match works, from Make Use Of: https://www.makeuseof.com/what-is-itunes-match/

Hi Arthur,

I understand where you're coming from. I too am quite particular about exactly how each track in my library should be presented, though I appear to have had better luck with iTunes Match and Apple Music than you. When I decided to try iTunes Match initially, which I later switched to Apple Music, I created a separate library so that I could take things gently, and would always have my original library to fall back on if required. Generally iCloud Music Library accepts my version of metadata, but for purchases where we disagree about the exact casing used only I have had to hide purchases from my purchase history to prevent Apple's version coming in as it attempts to integrate my unhidden purchase history with the rest of the library. Taking this approach means that my iCloud Music Library operates consistently across a number of computers and devices.

tt2

See Use multiple libraries in Music on Mac - Apple Support.

tt2