The bottom line is that the lock assemby is held in place by a flat retaining clip that is very similar in design and function to the clip that hold the breather filter in the air cleaner on my GM cars. Find a GM car, take the lid off the cleaner and you'll have a good idea of what I mean and how it works. BTW, it takes a bit of effort to slide it off the lock assembly.
Basic steps in getting to where you can pull the clip:
1) Using a thin flat blade, like a stiff pallet knife, pry the plastic grommets out of the fiberboard that covers the underside of the hatch. If you're careful they will all come out without a scratch.
2)You will see 2 screws, they hold the lock/unlock solenoid in place. Remove them and lower the solenoid.
3) Now it can get a little tricky, depending in part on how big your hands are. If you have big hands you may have a problem. The solenoid connects to the back of the lock via a rod about 1/8" thick. One end is an "L" shape that goes into the solenoid lever and is held in place via a molded nylon retaining clip. The other end is "J" shaped and goes through a nylon grommet in a lever attached to the back of the lock barrel. Both are difficult to unhook.
4) I had best results (after several tries) by pulling the clip off, lifting the solenoid assembly up and the lock partially out, then slipping the "J" end off the lock assembly. Using a small flashlight, look up at the clip and see where the raised end is. Using the "touch and grab" approach I was able to grab the end of the clip with a pair of mini channel-lock pliers and slide it out; i.e. sliding it flat across the back of the hatch to the left. The angle on the channel lock was important, I couldn't get a grasp with regular pliers - not enough room.
5) Putting it back together. Remove the connecting rod from the solenoid. Slip the "J" end through the back of the lock - put a heavy dab of grease on it so the damn thing won't fall out - and insert the lock partially into the opening. Then slide the solenoid up and feed the "L" shaped end through the lever on the solenoid. Then struggle to latch the retaining clip. Pull the lock all the way in and inser the retaining clip. Reattach the solenoid and wires. Done.
This little job was a real pain in the butt and took over three hours, including the time required to swap the cylinder into the assembly. The die cast lock assebly is a poor design; everytime the solenoid locks/unlocks it slams a steel lever against the thin diecast wall that retains the lever. I could see stress cracks on the junk yard replacement in the same spot where the original broke.
So I put an external steel "O" ring around the end of the assembly and using the holes in the "O" ring crimped a stainless wire safety loop around it. Since a had an "O" ring big enough that part only took about 10 minutes start to finish. It made for a tight fit getting the lock assembly back through the hole, but it did fit (barely).
It MIGHT be possible to slip a small stainless hose clamp around the end to reinforce it before it breaks. I'm going to look into that on mine when the weather gets warmer. If not I will probably tap an on/off switch into that line. I don't need to unlock the trunk everytime I get into the car and I certainly don't want to go through this nonsense again. (Bear in mind I also had to find and remove the junk yard replacement assembly - my FLM deal said the part wasn't available; course he's usually wrong on the first try unless you give him the exact part number)