eBay charges a fee for adding a subtitle to a listing. $1 for an item under $150. $3 for an item over $150.
1) Click on "Manage Inventory" under the 'Inventory' heading of the Control Panel.
2) Search for your item by it's Item ID (or Author / Title)
3) Scroll down to the 'Search Results' and click the 'Edit' link under your item.
4) Click on the 'eBay Properties' button.
5) Scroll down to the 'Listing' heading and next to 'Subtitle' edit your eBay listings subtitle.
6) When you are finished, be sure to click the 'Save Properties' button to finalize.