addvertex() on existing line?

[Krion]

Hi,

I am trying to recreate this:

https://entagma.com/procedural-subdivision-curves/

But then after primitves have already been generated. (I do this for technical, project specific reasons) 
This means that I run it on a Primitive Wrangle instead of a Point Wrangle, and try to use addvertex() after the addpoint() function calls.
But this does not create the vertices on the extant primitve. Instead it extends the primitive. 

I've tried messing about with setprimvertex(). I've tried to remove the verts already extant so the prim would disconnect (https://www.sidefx.com/forum/topic/59183/) but both didn't work for me. 

Is there some way I can create those vertices on the existing prim line or disconnect the prim before placing the new verts? 
I know I can remove the prim and start again with a new prim, but I actually need the 'new' prim to be the same @primnum as the currently processed prim. That's important.

Here is a sample hip: dingi.hipnc

 

Hope someone can help.  

Thanks.

Edited December 13, 2019 by Krion