Any Grid elements can be stretched with Pet palette commands: select the Grid Element, then choose the Stretch icon.
Select a Grid element. Click on the editing hotspot which represents the staggered part of the Grid marker, and then drag the Marker, together with the staggering length, to a new position.
The horizontal position of a grid element can be edited on the Floor plan and 3D window only. Select the Grid Element and use the familiar pet palette commands and shortcuts to Drag, Mirror or Rotate the Grid element, or copies of it.