I am aware that one can view the system's mapping of MIME type to file extension via: defaults read /System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist MIMETypeToExtensionMap.

I am also aware that one may indicate which MIME type (or file extension) an app supports via its Info.plist (or indicate which MIME type or file extension maps to what default application in LaunchServices).

However, I'm unclear if there is any way to application-agnostically indicate a mapping of MIME type to extension without modifying /System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist (which I presume is a no-no on what is possibly an auto-regenerated file anyways).

Or is the only accepted way to do this for an app to set UTExportedTypeDeclarations with a UTTypeTagSpecification defining public.filename-extension and/or public.mime-type value(s), with all built-in mappings being defined within MIMETypeToExtensionMap of /System/Library/CoreServices/CoreTypes.bundle/Contents/Info.plist?

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