Smart Group Using Extensions beyond those listed

I’m trying to build a Smart Group to collect all of the Excel documents in my database. We use .xlsm files for our Pricing tool as there are a bunch of macros in the spreadsheet and the files need to be stored in the xlsm format. My problem is that the only spreadsheet choice for the Extension option in the Smart Group builder is xlsx. Is there a way to add xlsm to the list so that I can gather those into the same Smart Group?

No, this is not possible.
You could use multiple Filename criteria in a smart group or Advanced search, like this…

The list isn’t predefined, it contains all extensions found in your database(s).