Can I have two SKUs under one ASIN? Both SKUs for FBA?

My item has a shelf life, and I want to have a way to sell old stock first before I send a new stock, but also without the ASIN going out of stock (I'm the only seller of this ASIN on Amazon).

Therefore, I kind of have to send a new stock before all the old stock sells.

But when I do that, I realize that Amazon starts to sell from the new stock before it sells off the old stock, and in the end, it's left with "expired goods" from the old stock just because Amazon didn't send off from the old stock first.

So to prevent this I want to perhaps create two FBA SKUs under the same ASIN, maybe price the two SKUs differently or something, and make sure that the old stock sells first before the new stock sells.