Is there a way to allow an expressly set parent date to turn back into a rolled up date?

[Robert Finkbeiner]

An Epic has been given start/end dates, but they are not dictated by the business.  Over the course of filling out the plan, there are more issues in that epic than can be completed in that time, and some of them have crept beyond the epic end date.  I can reset the epic end date by hand, but is there a way to allow it to roll up from task end dates automatically.  

It's so easy to inadvertently click an express time span into being, but there doesn't seem to be a way to un-express it.