Yes. To customize the subject line, click the Newsletter or multiple Newsletters that you would like to update and select Edit next to the current subject line. Once you click Edit, modify the text, and click Save when you are done. 

You can also add a customized Introduction Message by clicking "Introduction Message" on the top of the Newsletter(s) draft preview screen. Introduction messages can include links and will include the customer's first name if it exists in Engage. 

Personalizing each issue of the newsletter with an introduction or teaser "in your own words" can boost engagement and really give the newsletter a personal feel.