How complex is the rear trunk lock mechanism? The key will no longer go into it and lubricant hasn't loosened it up. It looks like a simple device, but can it be disassembled? I compensate with the interior trunk release, but if that goes, I'm out of luck.

 

Your post was moved to its own thread; so, as to not hijack a different topic and thread,

What year, model, and 2-doors or 4-doors? There is a slight difference for coupe vs sedan.

 

if this is for a not so compled Honda civic. the cable mech from inside is much more friendly and reliable.
the key lock mech is most likely stuck locked. if you can open the trunk.
remove the panels to access lock. you can remove the lock mech with about 3 10mm bolts(8mm but uses 10mm socket)
maybe remove it and soak it in seafoam. they are very cheap to replace though. used on ebay usualy $10