Now that Mura has been using the new CKeditor (formerly FCKeditor) , I have been looking at the various configuration options available: 

http://docs.cksource.com/ckeditor_api/symbols/CKEDITOR.config.html

These configuration options can be added to your styles.js.cfm , stored in the Mura file structure at
[siteid]/includes/themes/[theme]/js/editor/