Ok we progress but your volume is made by a Sweep or made by any other method ?

Because if it's made by a Sweep any modify of the rail (s) will made a new volume in real Time :)



If you want Control Points on the curve (rail) : Select the curve (rail), Press Tab , write Rebuild and enter number of Points wanted
Relaunch your Sweep, Move Points etc...

Ps If you Modify the Profil Start / End that will works also but only with generic transformations (move, Scale etc...)
not with a total changement like a "D" to "U" !