Quote from OK465:
"The first obvious change in Valphamax occurs when your wrist gets sore and push forward on the SS resulting in Valphamax noticeably decreasing as the aircraft is unloaded. 
"
Yes, perhaps you need to alternate between seats! (Being right-handed, I tended to over-control initially on my occasional visits to the R/H seat.) Any further info on variations in Valpha-max (or lack of) would be most helpful.
Returning to the
planned Habsheim flypast (at alpha-max, with thrust effectively controlling VS/FPA while the EFCS adjusts pitch to maintain Valpha-max), I've had another look at the degree of control available to the "PF". As you say, if his wrist gets sore and he releases the stick, the a/c pitches down to target the new AoA that the stick has commanded.
If the PNF leaves the thrust constant, the IAS will increase to a figure higher than the 1g-Valpha-max. So, as the PF pulls the stick fully back again, there will be a slight excess of IAS available to flare the a/c as the alpha-max is restored. Until the speed bleeds off again, the lift will be higher than before the disturbance, enabling a climb. In other words, it's the old story of potential energy being converted to kinetic, and then back to potential again.
However, the above scenario illustrates the potential for dis-coordination between the two pilots. As Confit says, the PNF's task is to adjust thrust to keep the VS zero. The PF has initiated a descent by allowing the stick to move towards neutral, but the PNF doesn't know that. Therefore, observing the undesired descent, he is likely to increase the thrust just as the PF is flaring the a/c. The thrust increase will have to be reversed immediately if the a/c is to be prevented from overshooting the 100 ft target height because of the increase in total energy.
Had this pilot-duo ever practised the manoeuvre
ensemble?