Good luck bricking your device then

I still don't completely understand if the following quote refers for zeroing out certificate or just changing it, but if it's the former, then perhaps after some testing it's possible to make an app for downgrading for the eager ones. (not that anyone expects upgrades from Nokia anymore )
P.S. Can you compare your certificates with one in my tar.gz (matching the version of course)? I wonder if it's dependant on the phone indeed.