Changing decel value of SUMO in real time using traci C++

[maths soso]

I am working on a V2V simulation where the acceleration and deceleration of a vehicle depend on the its speed. 

I would like to change the decel value in real time, I believe the way to do it is to put the following instruction  inside the "handlePositionUpdate" method in TraCIDemo11p.cc src file :

mobility->getVehicleCommandInterfarce()->setParameter('decel', #number);

I am not sure if this is correct since it is not working. I check the value right after setting it using : mobility->getVehicleCommandInterfarce()->getDeccel().