Wonderful : the trick of the rebuild works like a charm!
Excellent! :)

The "move point" method works also but is less practical if you want not a deformation before the extrusion...
The move and take back of a control point is some acrobatic :)
Draw a point or a line as a mark , move the control point and take back, kill the marks...
Extrusion
Not a big deal...but ...or maybe there is more simple...easy if your control point is on the grid... :)