Unless you are implementing custom code to create a Excel file object and manipulate/write out your data into it, I do not think any OOTB excel generation feature in Pega would allow you to do this. Any kind of requirement e.g. applying a diff format/color etc. in my mind would be treated as a manipulation to be done in the Excel file outside of Pega context using macros/formulae etc. I'll let others comment on they think about this as well. Thanks.