the 747-400 does have flap load relief through the entire airspeed range for the flaps. we apply hydraulic pressure and pitot statics in the hangar and ramp up airspeed - the flaps have strict airspeed tolerances in which to move up (can get these from the Maintenance manual if you really want them) - there is no warning in the flight deck when this happens, the system is entirely automatic.
If you exceed the red line on the PFD tape in normal clean flying conditions, you will get a red overspeed warning on EICAS, a red master warning (line of sight) light and an aural warning.