Blue Pump Override
There are 2 blue pump switches. The one in the HYD overhead panel will turn off the blue pump, even in flight and no the RAT will not deploy! This switch is not guarded!
Blue Pump override in Maint panel (Guarded)
As it's name suggests if you push this the Blue pump will be activated, where it would not be normally - So on the ground without engines running setting the blue pump to OVERRIDE will power up blue HYD and then things like FLAPS/SLATS, FLIGHT CONTROLS all become powered and able to move and create damage if not kill. Setting this to off, will turn off the pump if both your engines are off and you are on the ground.
This is why the yellow electric pump is also guarded! You are simply powering the flight controls and SLAT/FLAPS creating danger, which should be assessed from outside the aircraft before powering these systems.
Hence the call on interphone "Confirm clear to pressurize?"