have you tried hitting a small, sharp screwdriver in with a hammer to get purchase? then just turn it out. those things are pretty soft. take the caliper off if you wanna avoid any possible damage but you should be able to tap it in ok.
Pan - yeah - I’ve got the same brakes on mine and these little buggers seize in place if they haven’t been copper greased as you say.
All it should take is a centre punch and a hammer. - Put the centre punch at a 45o angle with the punches point in the groove at a position where when you start tapping the punch with a hammer the force will turn the grooved cover thingy anti-clockwise - put some penetrating oil on it and start tapping - it should eventually start turning.
Annoying little bastids those, always used to seize on my Hornet too, whether they were greased or not. Impact driver sorts it in 1 second though, the very reason I now have 1 in my toolkit.
The things are actually dual-compound like tyres - the bit that has the thread is made from cast-iron for its ability to corrode into the caliper, the outer layer with the screwdriver slot is contructed from a mix of re-processed cardboard and cucumber so the slightest force b*ggers the slot and you can’t get any purchase on it.On the VTEC I’ve replaced them with stainless ones with an allen key socket, only cost a couple of quid and worth every penny.