"Thick" edges is a profile edge. It does not split a face.
"Thin" edges is a face cutting edge.
SketchUp does not know how to split an edge with another edge.
Every time you complete a closed loop of edges that are coplanar, SketchUp will generate a face. You can delete a face, but the edges will remain. To re-create the face, just retrace one of the edges (there is no "Face" tool).
Drawing a close loop of edges in top of another face "splits" the faces - you'll have two instead of one, and they can be manipulated (extruded) independently.
- Select: Space
- Pan: ?
Change the Size of an Existing Edge
By extrusion: calculate how much you need to move (positive or negative), select the face for extrusion, and type the offset. It worked.
Change Unit to be Inches Only
Window → Model Info → Units
Move and Copy
Select → Move tool → Move while holding Option.