The Internet of Things (IoT) is a network of physical devices and software entities that interact together for fulfilling an overall objective. Such applications are built by selecting and composing several objects. Recent frameworks promote the use of 'if event(s) then action(s)' rules to make explicit the way these objects interact together, i.e., if an event is raised, then an action is triggered. IoT applications are not monolithic applications built once and for all. In this paper, we focus on the replacement of an object, operation which is often required for substituting an out-of-order or obsolete device. When substituting an object by another one, the user may want the application to provide at least the same functionalities as before. Therefore, replacement should be supported by automated techniques and tools in order to guarantee the preservation of the application behaviour. As a result, we first define several notions of object substitution. Then, we show how these notions can be automatically checked or computed. Finally, we present the tool support and its integration to the Mozilla WebThings platform for applying our approach on smart home applications.