Enhanced operation agility is now required from dispatchable generation means, hydro being top of the list. Increasing flexibility of legacy PSP has been implemented at Grand Maison scheme so as to provide regulating power in pump mode thanks to hydraulic short circuit technology. Extensive studies have been achieved to wave operational risk and provide operation boundaries. After 18 months, the demonstration has achieved 2500 hours of operation with full implementation onboard the EDF generating fleet.