Couldn't it be done on-demand? Apple orders X hundred boards, motherboard manufacturer makes their small modification(s) to a line that is currently producing t

Couldn't it be done on-demand? Apple orders X hundred boards, motherboard manufacturer makes their small modification(s) to a line that is currently producing the same models of motherboard as Apple ordered, they produce a handful, then they revert and mix in a few of those modified boards into the real order. I don't really know the exact scale, so maybe they make a few hundred / the entire order with chips in them, but economic cost isn't a big deal for things like this, so even losing money making the modified boards wouldn't be the end of the world (and presumably they get a hefty sum of money for whoever is paying them to do this). I thought China was famous for extremely short turnarounds for industrial engineering edits, so it seems plausible that they could manufacture the boards in a reactionary way and not need to do much in the way of logistics to get them to their targets.