Hello MO,
this technique is once again amazing. THANK YOU SO MUCH IN DEED !!!

I was also able to achieve the asymmetrical pull of the backrest — wow.

My formal goal, and what I need to change, is the seat. It MUST become dome-shaped later on. First i need it straight flat. Then I guess new splines brings the shape to the dome.

Some points on this way....
1 The seat is deformed/included in the current base and target surfaces.
2 That's why I wanted to cut off both surfaces from bottom - exluding the down meshpoints. (see a in picture attached)
3 What I can't manage is to remove the ghosted points after cutting—because I think they still influence the seat surface. I cannot hide them with the "rebuild" command. (see a in picture attached)
4 Remaking both surfaces—I can't even manage something as simple as that—how do you divide the mesh points? (see c in picture attached)
5 How do you retain the flow history so that you can still bend the shell by deforming the target surface after executing the command?