I also think is better to use more realistic stiffness numbers for supports instead altering the global stiffness. We had the same request from Structural Dept to lower the loads and one idea was to change globally the stiffness. Note that Autopipe use 10E+10 instead 10E+12. For big sizes it makes a difference. You will see some displacements into the supports you deem rigid, but most important you will see relative displacements between Node and Cnode.