Varying stiffness of gridshell lines in dynamic relaxation

Hi everyone,

I am doing a dynamic relaxation for a gridshell structure used for a library but I have some areas with a too small height and others with too high height. I was thinking of playing with the stiffness of the lines of the mesh: increasing it where I want it to be less deformed and decreasing it in the opposite case. I tried to do so by just adding a second spring box kangaroo component but it does not work...

I have joined a perspective view of the mesh after relaxation and my attempt of the modified script.

Tnx in advance!!

PS: I m a newbie here and posted this message in other categories but without any reply to my question, hope I can get an advice here :s