this should be relatively easy to do
how about the way you are handling the "Email registrants" process?
export order of the fields simply has the option to "save as template"
so that we can simply choose the template (predefined order of fields) and export
another thing - MUST BE: changing of order of fields in the csv export filed list
/index.php?option=com_dtregister&controller=export&task=fieldlist
saguaros