The other carb come apart fine, but this one decided to be problematic - and it's for the top cylinder, which was running lean, so that's probably a sign...
Unfortunately I'm not really kitted up for drilling something out - no drill, no vice (yet). Easi-outs can cause their own problems, too, though I don't see any other option here. I think I'll probably get a pro to look at this.
Thing is, I don't even think I needed to remove that as it is an air jet and unlucky to be replaced - and I'm having a very hard time trying to find it online, definitely doesn't seem to be a part that anyone ever removes. Too overzealous with the disassembly!
In saying that, it's only the slot for the screwdriver that is damaged, so I could just leave it. Of course, I can guarantee it'll cause problems if I do that. Do it properly. Just gotta track down a replacement somehow. I know it's called an air jet/nozzle (based off a parts diagram I managed to find in German which listed it as "Luftdüse"), but when I search all I can find is reference to the air jet in the intake bell mouth.