Fold a poly, procedurally create "crease" edge

[guache]

I have a long, rectangular poly which ends up "folded" by 180 deg (not necessarily in half, as in the pic). After folding, this poly is obviously very non-planar. I want to add a new "crease" edge along the fold line to fix it. I can create the edge manually in the viewport, but I want a procedural SOP solution. The Divide SOP seems most logical (Convex poly: ON, Triangulate non-planar: ON), but it doesn't always work. Sometimes it creates a new crease edge, sometimes it doesn't (maybe because folding by 180 deg is so radical). Is there a SOP that would reliably do this? I see a "Crease SOP", but it doesn't create edges, it assigns weights to existing edges. PolySplit SOP could work, but the way you need to specify the split points (% of edge length etc) seems unnecessarily complex. I do have the 3D point positions of the fold line, so I can easily create a line there. But how do I "plug" it into the existing poly as a valid new edge?

 

[anim]

you can use Knife SOP (or Clip SOP) 

also you may want to do several parallel cuts and then use Bend SOP spanning those segments to create some nice arced fold, so that there is some gap between top and bottom after folding

[guache]

Thanks. I'll try a Clip SOP, with the clipping plane aligned to the fold line, but set just a tiny, tiny bit "into" the polygon. so that it's guaranteed to always create an edge.

[anim]

You should use Clip to generate that edge before folding, not after