Hi,
--> Is it possible to run it in background : Yes
Try to launch your SE80, and you could see you could ask SAP to launch it in background (in the menu). So try it, go in SM37 and check the program and the variant.
--> Is it possible to change the date : Yes
When you have the program name, you go in SE38, you go in the variant option, you create it. In the option of the variant, you could define a date field as dynamic and specify : a calculated date, a TVARVC variable.
--> Is it possible to copy the result and change it : Yes but forget it
Have a look of this doc, you will see you could catch a result of a report : Sending Mail using Oo (3) - Result of a report
good luck
Fred