The paper considers the problem of the operation maintenance of complex soft- and hardware systems, for example, automated control systems of industrial objects, when individual components of the system become unavailable for replacement in case of their failure or for other reasons. When the replacement components differ from those that were designed at the system creation stage, the upgrade task arises. System upgrades require a complete cycle of work on validating both the replaceable components and the changed system itself. The system itself, if it is included in the life cycle of an existing industrial object, actually cannot be used as a testbed of the new components; generally, full-size system layouts are used for the testbed, and the complexity of those layouts may be comparable to the system itself. The inclusion of the digital twin in the life cycle of the object and its control system allows to effectively solve the problem of system modification (individual components replacement) in this case. The digital twin is not only a cheaper analog of the system that can be used for testing; due to the properties that allow parallel testing for several copies and to influence the model time within certain limits, it provides a higher quality of testing.