The purpose of folders in Crystal Enterprise is to organize reports, not instances of the reports. When you display the history for a report, the instance date and time are displayed. If a date parameter is entered, it will be displayed. There is also the option to View Latest Instance.
So I don't see any way you can use the folders differently. Your model does not match the CE model, but again, see the other thread mentioned above.
If the report itself is generating the date that you want displayed in CE, I don't know of any way at all to do that.
If you modify the csp, it will affect every report unless you can make the code conditional on report name or id. Given the previous answers, I don't think you want to go this way.