Ok, the "no-one" bundle-id was from the FakePCIID_Intel_X540-AT2.kext Info.plist - I replaced that with "rehabman".
I then removed FakePCIID_Intel_X540-AT2.kext from /System/Library/Extensions and reinstalled it with kext utility, and rebooted.
FakePCIID now loads, and there's a new ethernet card in System Information! However the new nic is not visible in Network preferences, and grep -i smalltree /var/log/system.log' still returns:
Feb 9 19:39:10 localhost kernel[0]: SmallTreeIntel8259x probe b3d0f0: Unsupported Card 0x0002
UPDATE:
I edited the Info.plist of FakePCIID_Intel_X540-AT2.kext again, this time reverting to:
<key>CFBundleIdentifier</key>
<string>org.no-one.injector.Intel_X540-AT2 </string>
but leaving:
<key>CFBundleIdentifier</key>
<string>org.rehabman.driver.FakePCIID</string>
then removed, reinstalled, rebooted.
The ethernet card now shows up in Network preferences! YAY! Unfortunately I can't test the native 10G speed, as we are waiting for CAT7a cables, but I will report back here with results for sure.
Thank you so much for the help and patience!
PS: Is the FakePCIID.kext part of MultiBeast? Searching for it on google only returns:
https://github.com/RehabMan/OS-X-Fake-PCI-ID
Of course I have the files from the-darkvoid in this thread, but just wondering.