ModifyCurve
Flexibility
The Curve Flexibility command enables you to increase the degree and/or continuity of a curve without changing its shape or position in space.
The new curve is more flexible because it is described by a larger number of control points. It is therefore easier to modify it, especially by making local changes to it.
If the selected curve is a specialized curve, you are warned that it will be converted into a NURBS and asked whether you want to continue (unless you have deselected the Ask before converting check box).