Blender beta 2.8: How can I insert a rim on this flat edge? I would like to double the amount of vertices along the edge, with faces, to form a kind of "rim" or "depth" here. What type of 3d operations do I need to perform in order to do that?
Select all vertices of the rim, then press E,S and move the mouse to scale inwward the new extruded faces; left click to confirm the scaling. Another method is to add a solidify modifier to the whole mesh.