Oh, so you are still having a problem with Drag from palette to diagram is not showing the shape ? Have you tried putting both the Palette and the target Diagram in the same component?
Back to this topic. If when the user drops a node on a link, you say that you insert the new node between the linked nodes. I would think that this should normally result in a layout being performed, to make sure that there’s enough room for the new node and that it is positioned reasonably.
Even if a layout does not happen, the modification of the existing link (or, alternatively, the removal of that link and the addition of two new links connecting with the new node) would cause the link to be re-routed. So I do not see how it could be possible to avoid re-routing the existing link.