You can apply tagattr statements to things, for not only formats but to apply formulas:
style={tagattr='format:Currency formula:RC[-1]-RC[-2]'};
Taken from this page:
https://support.sas.com/rnd/base/ods/odsmarkup/excelxp_demo.html
I would however ask why, SAS can do any of the functionality of Excel so why not jsut do it in SAS and export it. If you using Excel as a tool to do other things, then use Excel to build the tool, and pull in output CSV which is exported by SAS. Don't try to drive one application with another, just pass data between them.