I must be missing something. How do you change the length or height of a helical coil in synchronous after it is created?
I don't know if you intend to make a solid body from this or not. If you do, I've found that editing solids in Synchronous is much more efficient than trying to edit sketches in synchronous. See the video for how I would do the edits you are asking if you make it a solid using the Helix command.