I just ran a few tests, funny thing is you can equip one Cyclops with two magical eyes - even if the first one blinds him - or a Master Lich with three.
Btw, you can give a magical eye to a Granite Cyclops without blinding him - two eyed Cyclops, yay
. But the game I used to make the tests uses an ancient version of Endgame Diversity, maybe it has been corrected recently.