Thanks Micheal and Burrman,

In fact the isocurve is similar to what I thought but not exactly :)
And I don't want to work like a subd model, just wanted to modify some shape. I didn't know that Tspline was just a way to convert your subd in Nurbs.
What I wanted to do is having a kind of freeform modeling without loosing the power of working with curves.
Instead of modifying the surface points you change the construction curves.

For example in the picture I made the shape with sweep, what I had in mind is that if I modify any of these curves after the sweep is done, the other curves follow the modification to fit.
At the moment I can do it manually and it allow me to have simple shape construction and a great amount of control while still having perfect surface curvature.