It seems Boeing recommends bleeding off headwind additives approaching touchdown.
c) How you can bleed off wind headwind additives approaching touchdown?
Easier said than done with the common result being most pilots ignore bleeding off the additives (for half the steady headwind component). In turn and especially in conjunction with the Boeing recommended policy of adding all the gust, this has most pilots coming over the fence with excess speed. If the aircraft is allowed to float as a result of this excess speed over the basic Vref, then the aircraft will land long. Depending on runway length in excess of minimum required this may not matter.
But if the runway is wet for example and thus less braking efficiency, there is a risk of going off the end. This risk is increased significantly where company SOP requires minimum use of reverse thrust for various reasons. Often those reasons do not stand up to commonsense argument.
Where Boeing recommend bleeding off the half the steady headwind additive it gives no guidance at what height to start the bleeding off of airspeed.
The reason for adding half the HW component stems from the fact that wind gradient caused by the slowing of wind near the ground starts from about 1500-2000 ft above which is what is called free-stream wind. In other words below this height the wind slows due to ground friction. By slowly bleeding the airspeed it accounts for the drop in wind speed due ground friction. Not very well explained I know.
Boeing give a hint under the adverse weather section of the FCOM when landing with ice on the airframe and recommend adding 10 knots to Vref plus other additives already applied - up to a max additive of 20 knots. Boeing goes on to say "bleeding off the 10 knots (ice additive) below 200 ft. This would suggest that the deliberate bleeding off the half HW additives should start at 200 ft. It is a tenuous example, but Boeing tend to be vague in such areas.