Nuclear Power Plants (NPPs) have been traditionally operated from Main Control Rooms (MCR) and Local Control Stations (LCS) using analog technology with hardwired indications, controls and alarms in spatially dedicated in stand-up panels and consoles. The modernization programs in existing nuclear power plants have been changing the way to operate the Human System Interfaces (HSIs) of these MCR and LCS during the past 20 years, with the use of digital technology for Human System Interfaces (HSIs). These control rooms are now known as hybrid control rooms. Without changing the actual layout of the existing MCRs, the operation philosophy is evolving in hybrid control rooms in two directions: • To sit-down consoles, where the operator, can monitor the majority of plant systems and operate relevant plant information without the need of moving, using visual display units (VDUs). • To screens in the existing panels, where the traditional analog components are replaced with screens (touch screens or operated with trackball). This paper will show experience gained in examples of design modifications where Tecnatom has been working in design and verification and validations, where they way to operate HSIs has varied in some way. The implementation of design modifications is a non-stopping modernization process due to obsolescence of the existing Instrumentation and Control (I&C), HSI and lack of spare parts. In this way, the typical design modifications being implemented in plants with the participation of Tecnatom and focused in the MCR will be described.