current implementation of point spring in PrePoMax did not yet take the advantages of nonlinear options CalculiX capabilities. It could be more powerful if these feature been implemented, modeling such as response of steel anchorage embedded in concrete or blind hole bolt can be defined explicitly without detailing in part.
maybe, graph of force-elongation can be similar menus like stress-strain in plasticity material available. Plot of graph by data selection also useful feature.
*edited
i forgot something to notify, probably it still has limitation for tension only nonlinear spring. Currently, implementation in PrePoMax used one node spring element and tension only spring is required two nodes instead. Connection problems of master nodes and group of faces possible to solve by coupling constraint type.