To help end-users mastering complex applications, it is often efficient to enable them to "replay" what they have done so far. In some cases, it is even more useful to enable them to modify some values of the actions they are replaying. However, while doing so, it very important to deal with the consequences of these changes on the remaining of the replay process. In this paper, we describe our models to enable replay of user‟s interactions and to manage impact propagation of changes during the replay process. These models are built upon traces, i.e. digital objects that enable us to record user interactions and to reuse them in different ways. We have implemented the replay process in a Web application called SAP-BO Explorer, an application helping business users to access large amounts of information. Our tool helps users to better understand the application.