bambuino:
I caught your reply in re a situation in which you have comms over nRF with model trains, but you did not elaborate further about sending codes to individual receivers.
I don't use nRF devices, but Cypress transceivers which I suspect are similar and may even be compatible with each other. I wrote about the process here.
Have you managed to get your two Arduinos talking to each other using the nRF transceivers?
...R