I would imagine once policy is changed based on commander's intent (SECDEF by direction of POTUS) it becomes a zoo to have to change all the downstream military personnel policy to reflect that, but I think you raise a good question, and I don't know.
To piggyback on your question, I wonder how much of the executive/senate 'responsibility' is just rubber-stamped by staff underlings when the DoD sends them (if they send the executive/senate this info, at all) info that says 'hey, we are changing the way we promote officers, here's the info.' I mean, do they really care? I don't know.
I remember when I was promoted and saw the list come out, all the names on the dozens of pages of promotions in each and every community both active and reserve. I thought, they aren't really scouring for my name and looking at my bona vides.
Now you're making me think. Dammit.