how does the mariner change as the plot unfolds?

I think the Mariner changes both in a literal and metaphorical sense. The men died after the Mariner shot and killed the albatross. The Mariner feels this sense of death in that his cremates turned into ghost zombies. It isn't until the mariner has his epiphany, courtesy of the slimy sea-snakes, that all living things are sacred does his re-birth take place. The albatross slips off his neck and the Mariner then spends his time cornering people to make them hear his story.