The sensors and the resolution of the NIKON Z 6 and NIKON Z 6 II are identical, so the same RAW development should work (provided the lenses are the same as well).
I checked, how the RAW support is installed on macOS 11. Previously, several system versions ago, the RAW support has been installed as separate files for each cameras in the RawCamera.bundle. We could simply fake an additional RAW support file and reindex the RAW support. This worked well with the RAW support for Aperture. But the separate files do no longer exist. There are still the directories for RAW support, but the RAW support seems to be hard coded into one file inside the bundles.
/System/Library/CoreServices/RawCamera.bundle/
/System/Library/CoreServices/RawCameraSupport.bundle/
/System/Library/Assets/com_apple_MobileAsset_RawCamera_Camera/
Tagging the RAW images with the wrong camera model name seems to be the only way to fool the system, but doing this, we are mutilating our image files. We should keep the originals RAW files safe and just modify copies, and rename them, so we are aware of the fact, that the files have been modified and can revert to the previous versions, if Apple is ever going to release RAW support for the Nikon Z6 2.