We try to use ngons for their faces, like the ends of a cylinder. You can use the command AddNgonsToMesh to combine additional planar sets that were more than one adjacent face in the SketchUp file. In Rhino we call edges that have unique vertex indexes for the faces that share the edge “unwelded”. You can use the command SelMeshPart to select adjacent faces up to unwelded edges.
The way edges on breps are in Rhino is very unlikely to change. That’s why I’m suggesting that you take the mesh route. While I don’t know what “soft flag” means in SketchUp I suspect it’s the analog of our “welded” edge. Where the face vertex indices for the faces that share the edge are the same.
I hope this helps.
Tim