Hi:
If you are you using TAGSETS.EXCELXP or other ODS destinations and Base SAS, then the way that ODS works is to completely rewrite or recreate the file specified in the FILE= option or the BODY= option. The only way to write to a particular cell or range of cells is to use named ranges and PROC EXPORT and/or the LIBNAME engine -- using SAS methods -- but these are NOT ODS methods.
Using Microsoft technology, you might, with DDE, or ODBC or OLE-DB be able to write to existing sheets/workbooks to a particular cell.
cynthia