I saw this post in the demonhades web from the author:
"One last note, to make sure everything is correct on your machine, if you make a change of MAC, remember that you have to be in a firmware patch to prevent the SYSCON checks. The change is real, so if for any reason the SYSCON done some checking in a version without these patches would give problems.
I say here that's why I specified that probe, and it worked for pearls, but take care always. The change CAN work in an official firmware, but make sure to have your old mac, and before making any changes to official firmware leave it as it was before, to avoid future errors. REMEMBER IT!
If you have checks from SYSCON you machine will shutdown as if you use a downgrade without lv1 checks disabled.
Forewarned is forearmed