Graph rewriting with one-to-many pattern matching?
Belatedly posting this answer:

This is called set node or multi-object matching. This is implemented in tools like Henshin https://www.eclipse.org/henshin/publications.php and described informally in http://www.cs.le.ac.uk/people/rh122/papers/2006/Hec06Nutshell.pdf, see 3.2. 

A more formal account is in "Formal foundation of consistent EMF model transformations by algebraic graph transformation."

Thanks to Reiko Heckel for providing me this answer 1 year ago.