Force Surface Refresh

I can access the triangle list in the surface structure, and alter triangle vertices directly, but am having trouble getting the surface to refresh and show the changes. I tried adding a triangle that used vertices (0,0,0), but that only works once, and then stops working. Any suggestions?

Try setting triangle count at offset 68 in the surface handle to zero and increment new total verts changed at offset 4 in the mesh header (at offset 644 in the mesh entity). Might do the trick.

Or, as I have just found

Set the vert count at offset 64 and the tri count at offset 68 in the surface handle to zero.

What????

It sounds like you have something, but I am not sure I understand.