So I was not able to get 10.12 to work with LarrinkinAus's steps. I kept getting the "
Failed to open macOS Installer. The path /System/Installation/Packages/OSInstall.mpkg appears to be missing or damaged." error. Nor was I was I able to get dosdude1's patcher to work (the drive would never boot).
I am using a Mac Pro 3,1 (2009, Harpertown). I
was able to find a very easy work around, but this will probably not be an option for most people as it requires more than one computer.
If you have access to a computer that 10.12 is supported on you can basically just do the install normally, then adjust the PlatformSupport.plist and pop the drive or copy the image onto your Mac Pro 3,1.
Example:
I popped two drives into a newer Mac Pro 5,1 (Mid 2010). I installed 10.11 on Drive A (this is just so I can easily adjust the PlatformSupport.plist). Then I used DiskMaker X to create a 10.12 USB install drive.
I then installed 10.12 onto Drive B normally. I went ahead and went through all the initial setup steps (setting up iCloud, creating a user, etc).
I then booted back into Drive A and opened up Drive B via Finder.
I went to the root of Drive B (my 10.12 disk) and went to
/System/Library/CoreServices/
I copied the
PlatformSupport.plist file to my desktop (since it is locked), then opened it with TextEdit.
I then mimicked LarrinkinAus's steps of adjusting the strings:
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31. Inside the file, go down to the last entry which will look something like this:
<string>Mac-942B5BF58194151B</string>
Replace the Mac-942B5BF58194151B text with your clipboard data which is your board ID that you copied in step 27. So it should now look something like
<string>Mac-F42C88C8</string>
36. Whilst remaining in the same file, scroll further down (it should only be a few lines down) to where you see:
<string>MacPro6,1</string>
change this to:
<string>MacPro3,1</string>
37. Save the file and exit
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I then copied the edited PlatformSupport.plist file from my desktop and
replaced the original file on Drive B.
Then I pulled Drive B (10.12) and popped it into my Mac Pro 3,1 and booted no problem. I used this patch:
http://swdist.furcode.co/ and then I was able to update to 10.12.1
Note: After updating to 10.12.1 I had to repeat the steps for adjusting the PlatformSupport.plist using my other computer.
I was also able to create an image (using Carbon Copy Cloner) of the now "hacked" 10.12.1 image and install it on other drives/computers (using DeployStudio, but CCC would work too).