The online ColdFusion / CFML community website
1) One way would be extract the data (using <cfspreadsheet if you are on cf9 or POI Utility if on cf8 http://www.bennadel.com/projects/poi-utility.htm ) then in cf9 you could have it as a query and simply update it or cf8 loop through and append.
Then you just rewrite out the csv/xls .
If you proceed in small steps it should be straightforward.
2) Here is a Ben Nadel tute in this area http://www.bennadel.com/blog/461-Creating-Microsoft-Excel-Documents...