Is it possible to ensure that no debris from broken spark plug insulator falls into the combustion chamber when changing an old plug?
Do you have a vacuum cleaner and some very small hose, that can reach into the cylinder? If so, take the plug out as usual. Once that's done, get the vacuum and hose (gaffer tape the hose onto your vacuum cleaner hose) somewhat like this. (Obviously, the hose going into the cylinder will be thinner, but same principle).
Once the plug is out, use the vacuum to hoover up any bits that drop in; Spend about ten minutes doing this, even if you're not pulling anything up, because this is a step you DO NOT want to mess up, lest you get a bent valve or scored cylinder walls. Pull the hose out every few seconds to see if anything is too big to fit through the hose but can be pulled up via suction. Once you've done this, hopefully, you've ensured everything is out of the cylinder and everything is clean. I'd recommend cleaning the threads for the spark plug with a rag or brush before you start vacuuming, as this is probably the best time to do it, plus you don't want the ceramic to get caught in the threads, causing permanent header damage.
Good luck, hopefully it all pans out well for you!