As people don't like object history to be destroyed when modifying objects, would it be good to make the original into one of the new objects? Either resize it into one of the objects or leave the original nodes and change the way to be connected across 1 original node( 2 if a single column/row) and new nodes accordingly. That would give it more of a 'split object' or more commonly 'split way' type of feel. Could indicate which new shape gets the previous history with a symbol in it in the previewer.