I would tell the agent from the beginning what you want to do. It may not make any difference in terms of amount of work for the agent but at least you will be giving them the courtesy of proceeding as best fits their set of necessary steps. I see no advantage in not telling the agent initially. I have done this several times and sometimes the agent has said "I need to handle these as separate transactions so let's take one at a time." On other occasions I've had the agent say "OK, let me figure out the easiest way to do all of this." The response will depend on the experience and competence of the agent. Some will see it as a major task they've not handled before and some will have been through it many times and see it as a pro forma exercise. You stating everything up front indicates your willingness to go through the process by whatever means necessary per the wishes of the agent. Of course, if they give you problems about what you know is the legitimate process of canceling and using the credits as you wish, then get nasty!
