Q. How can I customize the look of checkboxes that have been selected? I don't want to have a colored circle highlighting the selected box, but instead want an actual "checkmark" or something similar.
A. There's no native way to do this in the component, but you can simulate this via the use of dynamic labels overlayed on top of the individual boxes. While this will cause some extra work for validation and data export, it will accomplish this goal. The attached .mfd file shows an example of how to do this in a single event handler assuming field naming conventions.