I've had a look at the lock barrell before now to change on mine. I couldn't see any way of changing it myself, it can be done, surely, but I just wouldn't know where to begin. The lock needs to be upright position and not horizontal. If it is vertical then all is merry, you can just use the boot release lever. To remove the old one, there is a metal rod that clips into the back of the bootlock (Inside the bootlid). Unclip that, then remove the two 10mm bolts and away you go. Put the new one in, bolt it up and clip the rod into the new braket piece. Make sure you have the rear seats folded down so you can access the back should it go pearshaped.