Yes ... I know :-) and i have do this. I try to explain:
My start configure:
I run Bios F2 + Ozmosis 824 + Mavericks ... save Values in NVRAM without Problems: iMessage works perfectly
I run Bios F2 + Ozmosis 824 + Yosemite ... NVRAM Values are available and i Message works
Now i make a update from Bios F2 to Version F3 and Ozmosis from Version 824 to 894 ... This works, but i can't write to the NVRAM.
I give my Values in the DefaultOzmosis.plist and my connection to iCloud, AppStore etc. come back, but iMessage can't connect because
my UUID changed. I think. That is the reason for try to change my UUID per DMI.
At the moment I use: Bios F2 with Ozmosis 894 ... But the RAM Section in "About my Mac" is wrong. Only cosmetic ... i know.
But I want to try it perfectly to have. With Bios F3 and Ozmosis 894 the RAM is correctly displayed.