The macron or kahakō over a vowel does not shift the pronunciation. It means that you pronounce it for twice as long. The "e" in Hawaiian is pronounced more like the short e in bet even at the end of words or with a kahakō on it. The a is usually pronounced like the a in father, but for some words it does have a slight schwa sound to it, like in wahine or nani. An a with a kahakō would never sound like a schwa, though.