Thanks!
However, there only appears to be a callback for the 7 bit version:
Currently, the Lua callbacks are triggered for “low-level” MIDI messages. The reason is that the callbacks are executed as soon as the messages arrive. Detection of messages such as 14bit CC or NRPN is done one level higher (and later) since Electra needs to understand the context of the message (ports, channels, previous messages). I will look at the code to see how I could resolve that and add callbacks for 14bit CC and (N)RPN. I will add the idea on the list at Lua API - stuff to add?.