I have no idea if it works, but have you tried changing the DF settings to disable cave-ins, remove what you want to remove, save, exit, enable cave-ins, and start your save again? I generally set up my cave-ins to be triggered by a lever pull removing a support.
I can see why that might work, but unfortunately it's for a script mod with explosive weapons and I'm trying to get them to be able to "destroy" constructions during combat, rather than a specific thing I want gone.
ATM the script just does a check in a square around the point of impact and changes any walls found into floors.
This works well enough for my purposes, but messing about with this in the arena made me realize that it could leave stranded floating floors with no supports and so the cave-in would need to ideally be triggered straight away, either by manual invocation of the check or by utilizing an artificially created and completed "remove construction" job rather than changing tiletype.
Using the 'job method' I've gotten as far as creating the job (the construction is flashing), but I haven't yet managed to get it to complete artificially.
Thank you for your help nonetheless.
Edit: As an update to this, I've gotten as far as being able to complete a deconstruct job artificially and trigger the cave-in
some of the time, but I've no real idea as to what determines if it works or not.
Edit2: No longer bothering with the synthesized job stuff, figured out how to trigger cave-ins by setting df.global.world.cavein_flags[0] and df.global.world.map.map_block_columns[].flags[0] to true, seems to be producing small amounts of magma, which is strange.