How about engines which are already derated? Can this engine be limited to an even lower level?

You could further limit your engine output, for instance for a second time, if necessary to fulfil the requirements by installing Datum Electronics Shaft Power Meter and EEXI Control Panel Interface. Unlike rigid engine limiters, Datum’s EEXI system allows the vessel Master to retain full control of the engine output (for instances where safety is paramount, as defined by SOLAS), whilst still providing the essential data to support the regulatory needs.