Just to think through some aspects of the interface: at present, rows may be copied by Option-dragging (and of course dragging the parent includes the children.) It would be logical if Command-Option-dragging created a clone: analogous to a Finder alias. (Unless I am missing something, this modifier combination currently does nothing else.)
I am very reluctant to suggest anything that complicates the interface, but there probably needs to be a way for the user to identify that the row they are interacting with is a clone. At it’s quietest, this could be a checkbox in the Inspector, which could be unchecked to break the link. (For rows which are not clones, the checkbox would either not be present or greyed out: this would not be the GUI element for making clones, only for separating them.
Another possibility for a quiet indication would be an alert when deleting a cloned row or its children to remind the user that they will be deleting it in both places. This warning could be turned off for users who are happy to manage their own risk.
Finally, just as rows with notes are badged, cloned rows might have a discreet badge (optional?) to indicate their status. Users could of course choose to prefix/suffix/italicise row titles in whatever way makes sense to them.
I really hope you can find a way to make this work with OO Ken.