Adding a custom center image for macOS 11 document icons

The macOS 11 HIG says "you can also supply a custom center image" for the new system-generated document icons. Anyone know how?

Clicking the "Use system generated icons" checkbox (which, oddly, is set to a mixed state by default in Xcode 12b4) adds the CFBundleTypeIconSystemGenerated entry to the plist, but there does not appear to be a way to specify a center image.

The existing CFBundleTypeIconFile value is denoted in the UI as the "Legacy Icon", which I hope means that it will continue to be used on older versions of macOS.

Steve
Adding a custom center image for macOS 11 document icons
 
 
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