Understanding XMP Sidecar Files

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So in the past I always preferred embedding metadata into the actual image files. Then I got used to XMP sidecar files being made for HEIC files I get from my iPhone. Now I'm thinking about using the "Convert Metadata to XMP" command to create a sidecar file for every image that doesn't have one. Aside from having a uniform experience across all my images, I have a few questions.

1. I did a test run and it seemed PS7 modified images when it created the XMP sidecar file. Is this normal or can I turn that off somewhere so it doesn't modify the file?
2. Will PS7 write to the image when it updates metadata to the XMP sidecar file after its been created? If so, can I turn this off so it ONLY writes to the sidecar file? My backup software backs up every file that changes, so I'd rather it backup XMP files instead of a few gigs of images when I make some metadata changes.

Just as I was writing this I looked at the drop down menu in the "Synchronize Settings" section of the Preferences, and saw the option for putting XMP Storage Location to "Always as a sidecar file".

Does this mean it will ONLY and ALWAYS write out metadata to the sidecar and leave the original files untouched?

Thank you!

[jstartin]

Does this mean it will ONLY and ALWAYS write out metadata to the sidecar and leave the original files untouched?

I believe that is correct, but:
Read the Quick Manual - Cataloging (available from the help menu) p18.
Try it out on a folder of copies of your files, of all of the types you have, just to be sure.