If the Military non-locality BAH rate changes does it automatically change in an allotment that is already set?

If you are living in PPV housing yes it will automatically change to the different rate if it goes up. If it goes down you will continue to get the rate that was set when you reported. If you are renting a place out in town and have it set up on allotment and it isn't PPV then no the allotment will not change, you have to do that yourself.