Happy new year tupu,

it looks like a curve description by Bezier. I think Moi uses Nurbs. Nurbs can describe Bezier-Curves, but you need access to the underlying math (knot-vector, weights ...). The incredible Max Smirnov has written a Script for the DeCastellieu-algorithm. I've never tried it, but you can find it here: http://moi.maxsm.net/startpos/24.
In general every change on the control points of a Beziercurve changes the complete curve - means no local manipulation possible - only start and end stands still if not moved.

At the end I didn't understood your problem already, could you explain it a little bit more please? Especially the values 0.75 and 0.576.

Have a nice day
Karsten