I think Shad is right. Solemnly this is not making any sense. The eggs from ‘pre-brooding’ wont die except if they are really old.
Lots of people had broodies who hatched chicks on a secret spot. Or didnt change eggs in a nestbox. Its natural behaviour to sit a few hours every day before commitment. Very normal before a hen gets seriously broody and stays on the nest almost non stop.
The outcome is possibly not the best you can achieve if you don’t change the eggs, but the embryos wont die in the pre-broody stage when the hen sat on the eggs for a few hours, for a few days.
My sensible broodies and broodies all over the world sit a few hours for a couple of days, before serious /non stop commitment. And they wouldn't do so if it would kill the embryo.