GraphQL seems to go hand-in-hand with Relay, and there's a talk on mutations in Relay here:

https://speakerdeck.com/laneyk/mutations-in-relay

That might provide the answers you're looking for. It's worth reading all the notes as I think this is the best resource for understanding how React + Relay + GraphQL really works.

You basically use GraphQL with a payload (the data to mutate and the mutation type) to select what to change and what data is returned after the change.