MRT in OpenLb


I want to use the MRT model for a 3-d simulation. Looking at the 2-D example for Poiseuille flow, it seems that all the user is free to choose in Openlb is the component of the collision matrix that is related to the fluid viscosity. I am wondering where and how I can independently choose the components of the collision matrix for a D3Q19 model.

In addition, I am wondering what function to use for the MRT model with body force. I tried ForcedMRTdynamics and I was informed that it does not exist. I earlier used ForcedBGKdynamics and it was successful

Also, is it possible to work with varying relaxation times in OpenLB, for both the BGK and the MRT models?