Okay sounds like even deeper dynamo developing. It is also described on the developer webpage (https://developer.dynamobim.org/), but I didn’t found it before. Otherwise I wouldn’t have asked, but your examples helped anyway. 
@JacobSmall
After all these informations I would really appreciate if you could spare some time for a view extension, that is capable of solving my issue. Of course I want to offer my help, eventhough I have just advanced knowledge of java, visual basic, c# and matlab.
Here a video of what I am working on:
I create a surface and pick specific points which I substitute with “handle points”. At the moment these points only inherit the x and y values from the points they are replacing and get their z-value from the number slider as with this they are movable in the 3D viewer. The problem resolving from this is that they have the wrong height.
Here my dynamo file. I marked the position where I would like to assign a default value to the number slider in red.
ReplacePointAtIndexWithHandlePoint.dyn (142.6 KB)