Hi Bahi,
I love site modeling. I love it so much I have a You Tube channel about it: Su Knu Vectorworks Site Modeling - YouTube. Feel free to email me at suknulandscape@gmail.com if you'd like to discuss your project further.
I have problems if I try to duplicate or edit a string that's already in my project file. If I copy and paste another one from the original marionette file then I'm able to relocate the control point without problems.