Thanks for your explanation
NYSEAN1
Thus your title/heading is fully correct - to unlock from Yuki rom.
I guess I got excited thinking that meant unlock a "bricked" SD card, which has been bricked through an error installing a WP7 rom such as Yuki rom. The two issues are different. However, you have not claimed the later case, but the first, and that is fair enough.
I have always hoped that an Android system might resurrect a fully bricked card- I still hope, but not their yet.
Thanks again
Edit 1: BTW thanks for putting me on to ext4. I do like it!!!
Edit 2:
Seems like the only way for a bricked card is for a Nokia device (or similar), which I don't have. See
http://xdaforums.com/showthread.php?t=1242071