Up until this moment there was no solution - I had done the same crap and wound up with the same lockout issue - however I solved it thanks to some serious reading and experimenting - the solution leads through booting into shellx64.efi and running a dmpstore -b command - this will list all contents stored in the nvram - go through the list and look for variables ffm-computer-name, ffm-authentication-token-FFM, system-recovery-lock and other apple related variables and delete them with the command dmpstore -d variable name (e.g. variable = ffm-computer-name). Once you have cleaned it up exit efi shell by typing reset and boot into clover and osx installer - the 6 digit pin will be gone - and once u fix it don't mess with it again - took me 3 days to figure this out
P.S. Don't delete anything you are not sure about or you could wind up wrecking your entire UEFI system ... I haven't tried and I wouldn't - if in doubt - ask here.
Hey guys. Its actually pretty easy if anybody finds themselves in this position with Clover. I actually did this today at work too. Seems like there's a bug in Apple. Because I remember putting a 4 digit lock pin. The same as my Iphone. But I get home and find my mac doesnt boot. Luckily I tried my recovery partition and thats where I was presented with a 6 digit blank set of spaces for me to enter my code which was only 4. No way to get it to take just 4 digits and putting in more results in invalid code. So I read around a bunch of threads but mainly this one. This thread and your post specifically led me to an understanding of it all but still I couldnt figure out how you did it. Tried renaming the boot file to shellx64 but that didnt work. My system booted to windows 8.1 instead. Nor could I figure out what you did with the little bit of info in the message.
So I messed around and this time I selected my recovery partition but instead of just booting to it, I booted (with the space bar) to the single user mode option. This allows you to type "nvram -p" to see the nvram values, just like you mentioned. And with a quick search on the internet, I found that nvram -d value will delete the value you specified. So the 2 that looked like they had something to do with it were... recovery-boot-mode which was set to locked. and the other which I did first as a test was the actual lock message which in my case said "locked by don". I think that was under a "good-samaritan-message".
Anyway, again the steps where.. Select the recovery partition that clover sets up for you when you install OSX with clover. Select it but instead of pressing Enter, press the space bar which will give you a list of booting options. Boot to single user mode. Do the nvram -p to see the nvram variables. You will probably see something called recovery-boot-mode Locked. use nvram -d to delete that variable from nvram...
nvram -d recovery-boot-mode
And in my case I set the message when I originally locked it so I deleted that first. After both deletes I did a nvram -p again to see if the value was gone. Once gone I let the computer boot into recovery which happens after you exit out of single user mode. and this time no 6 digit code prompt.
You could probably do this with any of your boot partitions, I only selected the recovery one because thats the only one that my hackintosh showed a screen for. The other ones, my main and my backup partition just went to a blank screen. But when booting with space bar selection on an option, you can probably go to single user mode anyway as its not a graphical screen.
But anyways, hopes this helps some unlucky soul like I was. Now Im back and looking at pr0n again.