This is an early morning idea, perhaps inspired by clothoid and boxcutter/carver, so may not be practical.

Script to perform user interactive re-Blending of a curve, with the script facilitating the procedure, and automating it as much as possible.

Mode1:
Select 2 points on a 3D curve. Trim curve portion between points. This results in an inner curve with two endpoints,
and also, for a closed curve, one outer curve with two ends, or two outer curves, with two new endpoints.
For an Inner submode, blend the associated endpoints.
For an outer submode, blend the associated endpoints.

Mode2:
Select 1 point on a 3D curve.
Trim could be determined by a sphere radius, provided the sphere only intersects the curve at two points, Trim curve portion between points. Blend inner or outer endpoints.

Or Trim could be determined by an arc length along the curve in either or both directions from the picked point.

Version for surface/iso network/lineweb ???

- Brian