Is it possible to have subscriptions sent as a ".CSV" attachment instead of a ".XLS"?
If so, where does this setting get changed?
By subscriptions, do you mean Smart List subscriptions? You can change the format by selecting "Comma Separated Value" as the "Format" type when setting up the subscription.
As far as I know, you can't change the file type for Report Subscriptions. What is the reason for needing a .csv instead of .xls?