Can I include my alimony payments in "subtractions" on my NY return? (I think the rules changed in 2018, but I can't remember if they changed for federal, state or both)

You are correct they did change for federal but not for state. Alimony payments are no longer tax deductible for the person making the payments nor are they taxable to the person receiving the payments for your federal return, but they are still deductible for the person making the payment and taxable to the person receiving the payment for the NY state return.