Hi Debbie.

Firstly to introduce myself.  I'm the product owner for perform.

The short answer is no.  While the ability to edit a recent 'post' is a typical use case, there's a fundamental challenge to allowing users to edit content in a formal activity.  Particularly after the activity has closed.

This idea is being tracked here TL-15005.  I've added this feedback to that so we track your requirement.