Hi, with the boot lid open there are 2x access holes either side of the lock from one off these holes with the flat blade of a screw driver you will be able to get contact with a large thin metal spring "C" clip that holds the lock in place, it has a folded up part on the clip to push against. Have a look at page 92 rimmers catalogue part # 723290A YKC4530 looks the same for both lock types. Good luck hope this helps.
Hi Sorry about that, my lock has a small screw in the end that holds the white plastic locking part to the key barrel but it does look like its been modified! My factory manual only covers early twist locks, but if you push the button all the way in there are 2x small metal clips either side its possible they hold it together? but they could also be what holds the individual lock tumblers in place?? sorry I can't be of more assistance.