This post might only be a placeholder for some bpy. The snippet accesses a point on the first grease pencil object, on layer 0 and stroke 0.
bpy.data.grease_pencil[0].layers[0].active_frame.strokes[0].points[0].co >>> Vector((-4.293455123901367, -2.6403982639312744, -0.5711002945899963)) # and modify in place bpy.data.grease_pencil[0].layers[0].active_frame.strokes[0].points[0].co.x += .2 # to see the update you must do something inside blender # to instigate a redraw/update, i usually do a 3dview rotation.
