Aha I see, I don’t think Unreal Engine supports this kind of stuff, I would rather see if you could make the edges hard by marking the edge as sharp and setting that value, or adding custom split normals data.
I’ve never done what you’re referring to, but might it be this setting you’re looking for?
“Loose Edges” which exports loose edges (as two-vertices polygons).?
That is at least an export setting in Blender, but I’m sure any 3D software has their naming and version of this.