Based on my experience with remarketing lists, I don't believe the person will be removed when you set the new rule. If this is a remarketing list based on people who visit your website, then that new rule will be applied to the next person who visits the site after you've applied the rule. If a person in the site visits your site again and no longer matches the rule, they will be removed from the list. Otherwise, people will just fall off the list as their time on the list expires. Feel free to double-check with the
General AdWords Forum, since this falls into the category of a more general AdWords question.