Thank you for contacting us. Unfortunately, we have not implemented such functionality yet, but there is an existing feature request for customizing the board cards: http://feedback.telerik.com/Project/8/Feedback/Details/715-boards-card-customize-the-information-visible-on-the-cards
You can vote for it to increase its priority in our backlog.
Currently, there is no way to customize the summary in the preview pane either, but you can post an additional feature request for this.
Do not hesitate to contact us again if you have any other questions.