PlanetsCentral

yes, at auto task screen it is easy to do.

But I want to be able at the star chart to indicate to the ship the path of multi-turn movement that differs from a straight line and in result an autotask skript for the ship was created.

At this moment for a complex movement I must create an autotask skript manually.

Or
could I change autotask of a ship in a program?

I am not sure I understand you correctly: of course you can enter a non-straight auto-task on the auto task screen? Choose first waypoint, double-click (or Ctrl-W), second waypoint, double-click, etc. Optionally, using the 'a' window for each leg.

Auto-tasks don't really exist (as program objects) outside the auto-task editor, so most things you can do with auto-tasks need to be done on the auto-task screen. I'm changing that for c2ng, but that's still a long way down the road.

But since I'm currently trying to implement missing PCC1 features on PCC2, this remembers me that PCC1 can actually show (but not edit) auto waypoints on the starchart. Dang, another one to do...

--Stefan