Hi Joanna,
appreciate you posting the question. Unfortunately we do not support updating email templates for the background report execution feature. Your request does make sense and I can see this being a valuable enhancement for other Ariba customers. I would suggest you share your enhancement request by creating an ER (Enhancement Request) through Ariba Connect (https://connect.ariba.com). We will consider your ER when we begin planning our next major release.
Thanks again for posting the question. Receiving feedback such as this is extremely important.
All the best.
Manny Cortez
Ariba Product Management