If you need approximate deformation, then you can simply use a thin-plate-spline transform driven by control points in Slicer. It can warp not just models (meshes) but volumetric images and all other nodes as well. Here is a short tutorial how to set up something like this for a more complicated case (deform soft tissue with constraints of nearby bones; modify an image, not just mesh):
If you need physically realistic deformations then I would recommend to have a look at IMSTK. @Sam_Horvath can give more details about how that works in Slicer.
