You can change the subscribers to the category you are using in your campaign at any time by changing the name of a subscriber, removing them, changing information about them, or adding subscriptions.
Where do I find it?
You can view the list of email addresses in your Email Marketing Campaign by going to Services > Email Marketing: Campaigns, clicking on the Campaign's Name and clicking Campaign Category Subscriptions (ex., Newsletter Subscriptions).
You can also go directly to the Email Marketing Category by going to Services > Email Marketing: Campaigns, clicking Categories, then clicking the Category of interest.
From the Category page, clicking Category Subscriptions (ex., Newsletter Subscriptions) will show you the current subscribers to that category.