Re: Marvel Now/ReEvolution Ongoing Discussion (Spoilers)
Monica has been part of Carol's supporting cast in "Captain Marvel" and currently has no codename I believe. Ronin will be a new Ronin, there have been previously multiple Ronin's who have used the codename. The very first one was Clint Barton (that he used when Clint first returned I believe).
Chief of Operations
Ignoring the The Last Stand since 2011.