Is there any other way to rotate it in the current state other than editing mode?

How do I rotate that shape in Grease Pencil mode?

If i understand you correct you want to rotate around the yellow points without leaving object mode, right?

For this:

  • set pivot point to 3d cursor
  • set snapping to vertices or edge
  • hold left mouse button, move your mouse, then hold ctrl too -> so the 3d cursor starts snapping
  • then you can rotate and scale (keys [r|s]+[x|y|z]+(mouse move | [-]number))