I would like to change the "format" dropdown of the RTE to my own CSS formats. So instead of having "Normal" "Heading 1", Heading 2", etc. display, I would want to have "Body Copy", "Headline", "Sub Headline", etc. with my own CSS associated with each display. Is this possible to do? If so, where do I make that change?

Thanks!

format contains the standardized HTML structure elements for documents. 

If you want to provide custom styles, create your own fckstyles file (see www.fckeditor.net for details) and specify this to be used in advanced editor settings or generally as  \Portals\_default\fckconfig.js and adopt the appropriate fckeditorprovider setting in your web.config file.