The original spline following script that I posted is a"run-once to build the original object" command scripts, not a parameteric one. It could be installed as a command script or run explicitly. It doesn't work as a parameteric scripts.
The output of parameteric scripts are supposed to be entirely defined by their numeric parameters. That's why they can't access any other input (like look to see what other shapes are in the object, see what frame they are in, the time of day, etc.). If they could be influenced that way then they could look different when put into a scene, etc.
I suppose it's possible to keep the original spline as something like a lot of parameters but that's not anything Anim8or can do. You'd have to type in a whole lot of numeric values to change the shape of the spline. That's not something that any human I know could do in any controlled manner

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Another more likely possibility is to make a new kind of script - a "derivative object" script or some such name. You'd build a shape of some sort (e.g. a spline) and then attach a script to it. Whenever the shape was modified the script would be run. The base shape wouldn't be visible (except in the Object editor where you could edit it) but the result of the script would. I think that would do something more like what you want. Anyway it's an interesting idea.