Thanks for having a look at that scfreak.
I figured deleting enough of the units that weren't crashing the editor could possibly seem to fix the problem of being able to delete those that were crashing it, but I'm far enough into my own recovery plan now as to pretty much abandon any other course of action (besides a miraculous, quick fix).
The option I ended up going with was to copy and paste from the buggered up map to a new blank one. I took only the ones I really wanted (still, was about 200 or so), then imported that lot back into the buggered map.
Of course, it messed all the units up, and it has taken a LONG time going through the triggers to get back to the stage now where I can start repopulating the areas.
The funny thing is, I'd been doing things the hard way before. I didn't have to have multiple copies of the same unit if I wanted them at different static locations on the map. Provided each one has its own region, I can just set its custom value accordingly, and then use that custom value when determining where to respawn that unit.
It's been a painful process, but by the time I'm back up to where I was, the map will have less than HALF of the custom units that it did before. 530-odd down to 250 now. I guess, some lessons are best learnt the hard way.
Anyway, thanks again for looking at that for me :)