You are correct that a state can choose its OWN method of selecting electors.
However, the COMPACT that says that the state's method is contingent on other states in the COMPACT also agreeing to abide by the rules constitutes a compact among states that is in violation of Article I Section 10.
States can act individually. They cannot gang up on other states.
-PJ
Great Constitutional issue for SCOTUS ...
I was just pointing out what MD has on the books by way of the law ...