You're much less likely to screw anything up if you just leave them alone, than if you mess with them. Unless you smell a bad one, wouldn't worry about an egg exploding. An egg that far gone would reek, long before it blew.
That would also remove the possibility of culling eggs in error, that might've hatched otherwise. After your wave of hatches, on day 21, if all goes well, if you wait 2 or 3 days, til tou're pretty sure no more are gonna hatch, that's soon enough to discard bad eggs. And do egg-topsies, if you wish.